This is a hard question because each person is unique. A large percentage of vagina-owners simply can't orgasm without clit stimulation, which is perfectly okay! But if you are determined to get a G-spot orgasm, I would say experimentation is your best bet: pay attention to what vibration and thrusting speed gives you the most pleasure, what angles and positions hit your good spots, etc.; for example, in my case, I eventually figured out that G-spot stimulation works best for me when my partner is behind me or underneath me (which can be simulated by a dildo or vibrator with a suction cup) as opposed to a more classic position like missionary.
While you mention specifically wanting to orgasm with penetration alone, I'd suggest you try combining toys, since the combination of clit penetrative/G-spot stimulation often leads to the most powerful orgasms. If dual-stimulation toys like rabbit vibrators haven't been getting you off, you might try a G-spot vibrator and a separate clit stim vibrator, like an egg or a wand vibe. (I will also rep the G-rumble here, which I love for clit stimulation and can also be used for the G-spot!)
When trying to get yourself off, it's sometimes possible to put too much focus on the orgasm and, paradoxically, fail to get there because you're so intent on getting there. There isn't one sure-fire fix, but maybe try some bodily exploration without the specific intention to orgasm. It may also help to make sure you are completely aroused beforehand. Some people might watch porn, read smut, or just fantasize about what gets them going; some might incorporate foreplay, like a panty vibe or (if you're into something slightly kinky) a harness with a crotch rope, that will stimulate you while going about your day and build momentum for the big O.

Like ajin mentioned, this question is so hard to answer because everyone is different. For so long, I thought that I was only able to orgasm with clit stimulation, even using dual-action toys, I was pretty convinced that I was only climaxing because it the clitoral attachments. The big game-changer for me was getting a toy with a really nice curve to it that hit just the right spot, I actually vividly remember how different that orgasm felt compared to what I normally experienced.

From that moment on, I was on a quest to figure out what made that specific orgasm feel so much more intense, and I found myself researching g-spot stimulation. I purchased a very basic silicone vibrator that was curved but without the clitoral attachment and just started experimenting. I tried different positions I might not have tried otherwise, tested out different angles and speeds when thrusting the vibrator, and applied different levels of pressure. It wasn’t instant, I put a lot of focus on having that orgasm again and got caught up mentally and went back to thinking maybe it just felt different but was still a clitoral orgasm. Eventually, though, when I stopped trying and started to just focus on the sensation and feeling, it happened again and again and again. I still prefer both clitoral and g-spot stimulation for an intense blended orgasm, but it was an amazing learning experience figuring out my own body.

My best suggestion is to just experiment, both solo and with a partner. Try new positions, new toys, different amounts of pressure and speed, and just see how things feel. Don’t focus so much on the orgasm, but the experience as a whole - the more comfortable you are, and the better you get to know your own body, the easier orgasms come.

I must say...Bravo on the orgasm without clit play. There are millions possibly billions of women out there who would give there left boob to cum without having to have some sort of clitoral action...myself included!!
To answer your question I will let you in on my secret pleasure. I say secret because this "vibrator" really isn't a vibrator at all but a back massager. It is as old as me maybe even older and believe me when I tell you that the orgasms that I receive from this little slice of heaven are enough to make my toes curl and my ears bleed. (Kidding about the ear bleeding) Honestly I quiver at the thought of my back massager in my third drawer just laying there underneath my workout leggings and shorts waiting for me with open arms to fill my every fantasy if only for a moment. (sigh..)
Back to you!! I have found that the best way to achieve said orgasm is to lie back on my bed but have my shoulders propped up like you would if you were working on your laptop. Take your phone, ipad, tv, whatever and watch something that turns you on inside and out. DO NOT PUT ANYTHING INSIDE OF YOU. This will take practice and if you feel the need to cum and yearn for the D it will not work. You are trying to cum with clit stimulation, REMEMBER??Trust me when I tell you this. Softly put the "vibrator" on your clit. Spread your lips so there's plenty of room and start to massage it gently. Rocking your hips slowly you will find that with each position of your hips, there will be different sensations within your already swollen clit. By rocking your hips, you may find that one position that you like the best...THE BEST. Press harder on the "vibrator" eventually flipping the switch to FULL BLAST VIBRATION. For me... that's all it takes. I love that after the first orgasm I stand up for a minute or two, lay back down and place the "vibrator" back on my clit and instantly cum again with the same strength and endurance as the first orgasm. It seems if I try to cum again and I stay in bed only to impatiently slide the "vibrator" back onto my clit seconds after my first orgasm, I will cum!! It is never as strong as the first one though. It could just be the way my body works. Hell I'm happy to even have the one, but with that technique, I can cum as many times as I want each orgasm as strong as the first. GOOD LUCK.

P.S. Eden Fantasys sells
a vibrator that looks like my "vibrator". It's called a Wand Massager.