Just start off small. You don't even have to get an insertable vibrator at first, and get one supposed to be used externally. The thing is that you being 'tight' really isn't about you not having been penetrated very much, it's about you being nervous and not used to the feeling.

Here are a few suggestions you should look at:
Birthstones This is a very small, thin toy that you can use for very shallow thrusting. It's a great toy to use to warm up, and very cheap in case you don't like it.

Rocker Vibe 7 This toy is a bit thicker, but is longer and better for thrusting. If you're looking for g-spot stimulation it's a better bet than the Birthstones.

Diamond Fairy This is an adorable toy that can be used internally and externally. It's high quality, and isn't too large.

Icicles No. 8 This glass toy is very thin and pretty. It's great for people that aren't used to penetration because it has almost NO drag to it.

I personally hate girth at my entrance, so I totally understand wanting a thinner toy. Just another tip is that you should warm up before hand by playing around clitorally (using a bullet and such) to help things go more smoothly. Also:

Sliquid Sea USE LUBE!

Message me if you have any more questions. I just bought my first toy on Eden a few months ago, so I know how overwhelming it is just looking at the toys on one site, let alone the whole internet! less

Good advice, but don't go to the opposite extreme and get something too cheap and crappy or you might have a bad experience with it. Our first toy was a slim silicone traditional vibrator (unfortunately not offered on this site) and it has lasted for years even though it was priced in the $30 range. less