Welcome to the forum.
My best advice is to not run before you can walk. First look for a toy to try out at home, then consider one of wearing out.
When it comes to anal toys, size is in the eye of the beholder, what one person thinks is too big someone else will dismiss for being too small (even if both are beginners). When it comes to falling out, this is also partly an anatomy thing so again not every toy will work for every person.
However some toys I would suggest looking at to start with:
Smallest metal plug (I think) there are larger sizes available and a choice of colours in different sizes
This one and this one are very similar
Simple and smaller simple