How do I know which sizes to buy

As far as the sizes go, I would go under the recommendation of your gynecologist or whatever health professional directed you to these products.

Can i sleep with this in?

Ahhhh, I see said the blind man! You’d think with all of my fancy degrees ida picked up on the word, um, “dilator!” Duh! And YES! Absolutely blonde tee hee hee. So ignore the info on doing the kegel exercises as this will do the complete opposite!!! Funny, I assumed you put both the “weight” inside or a “dilator” for the same goal, nope! But please, do heed the warning on sleeping with this inside of you…. It just wreaks of infection and other medical issues. And still — good vag health to you all (us all)!

I see this product is returnable, so will I get a returned product? Will returned product be sanitized

This question is best addressed directly with the company. They are a reputable firm in Kansas City and will almost certainly be happy to answer your question.