I received my XL onesie from Baby Pants this last weekend. I had done some research, and from what I could tell, you're supposed to order your size and allow for shrinkage. Well, I'm super lazy, and went by my XP Medical bodysuit size, that being XL. Well, like many have mentioned, they are really generous sizing-wise. It was massive, and even washed three times, it didn't shrink to a size compatible with my body size and disposable diaper.
So, I did some more research, and found a site that said to boil some water, add the garment you want to shrink, bring back to a boil, turn the burner off, and soak the garment for five minutes. I'm pleased to say it turned my comeuppance from not properly measuring myself for this specific product, into near perfection. I say "near" because the butt is a little poofy, but all in all, it's a great fit.
I thought I'd pass this along, as I seem to remember a post where someone gave away a too-large BP onesie.
Now, the site also said once you do the boil trick ( only works on cotton, btw) your garment is "set" and won't shrink any more, so something to consider.
Anywho, I thought I'd pass that along. I almost gave mine away, too!