Onesie Sizing Help!

I am trying to find the exact size I need for a pair of Baby pants onesies before I buy them, but the sizing guides are confusing to me. I am 5' 11'' tall and approximately 260-275lbs (trying to lose some weight). My waist size is anywhere between 44'' and 46'' and wear large sized diapers (until my waist gets down to 42 or less). Your help would be most appreciated.

Im 6'00" and 165 lbs. my measurements are
Waist - 40
Hip 39
Leg (circ) 24
Chest 41
Trunk 70
1/2 Trunk 3

I just ordered two onesies from babypants, one small and one medium so I could be sure I'd get the right size. The medium was way too big, and even the small was a little loose fitting when I first put it on. I suspect the small will fit me just right once it's been shrunk in the wash a few times. When it comes to diapers, I tend to err on the side of going too large, whereas for abdl clothing, I find it is better to err on the size of going too small. I have found these to be good rules of thumb for getting the right sizes when I buy new abdl stuff.

It's proven to me through experience, with Baby Pants specifically, to go with one size smaller than you think will fit you perfectly.

Just be aware of your hip size. I am rather 'hippy' and ordered a 2XL from Littleforbig. I could probably do XL because I am short. May do for my next one.