I don't have a lot of anal experience - but we have a vibrating butt-plug from A&E
link. The vibes are really strong even though there are just 2 AAA batteries.
I've seen it advertised as silicone - but I'm not sure that's true - I've used a silicone lube with no problems.
This plug is 1.5" at the crest and about 5" long - so if your inexperienced like me - it'll take a little time to get in.
I don't know if it's the strong vibes or the relatively modest dimensions - but it can pop out after a while - if I can get just the right amount of lube - not too much - it'll stay in better.
But hey - by that time it pops back in pretty easily as well.
The vibes are strong - and I think that's what your looking for.