Plus Size Cheshire Cat Onesie Costume for Adults

Since you want a roomy fit and have fuller thighs, the waist and hip room in a onesie matters a lot, and the 2X has a 56 inch waist and chest with a 44 inch torso, while the 3X opens that up to 60 inches through the waist and chest with a 45 3/4 inch torso. The 3X might give you the comfortable, relaxed fit you're looking for. Measure your chest and waist and compare those numbers to the size chart to be sure you land in the right spot.
(AI Generated Answer)

A UK 18-20 converts to roughly a US 14-16, which would typically land in our 1X range, but at 5'9" the torso length is worth a close look. Our 1X has a 42 1/4" torso and 30" inseam, while the 2X stretches to a 44" torso, so if you're long in the body the 2X might be a more comfortable fit. I'd recommend comparing your own torso and inseam measurements against our size chart to find the best match.
(AI Generated Answer)

For a baggy fit at 5'5" and 246 pounds, the 2X could work well since its 56" chest and waist give you some extra room, but if you really want it roomy and relaxed, the 3X with a 60" chest and waist might be the better pick. Comparing your own chest and waist measurements against our size chart is the surest way to land on the right size for the fit you want.
(AI Generated Answer)

As costumes are not made like regular clothes, they are more delicate. Most of the time there's a tag with care instructions, otherwise, we recommend hand washing or spot cleaning and hanging it to dry. Please do not iron, instead, you would want to steam out wrinkles.