Thax's wife here Note I am not yet approved, but it's not due to my flight suit! Awaiting better fitting torso armor and remaking pouches, etc. to fit me as a short person.
It was pretty simple. I bought a Wampa Wear flightsuit, got the zippers positioned in the downward position (safety pinned down to keep from losing them), and just cut it at the waist with a pair of fabric scissors. I cut right beneath the elastic on the flight suit, so that stayed with the "jacket". I used a serger to finish the edges on jack and pants, though you could probably do pinking shears or zig-zag stitch if you don't have access to a serger.
For the pants I used some spare knit fabric to form a little tube to attach some elastic at the waist to keep the pants up better... as an alternative to this I could have cut *above* the elastic on the flight suit and it probably would have worked out great for the pants! I hand sewed around the zipper to close it off at the top. I also got some clip-on suspenders to keep pants up, but if you are typically seated in a wheelchair this may not be as much of a concern for you.
For the jacket, I attempted to install a new zipper... but I was pressed for time and didn't plan it out properly so it was poorly implemented. I am going to remove it and just sew in 1" velcro on the front for a closure. I attached the butt flap just above the elastic on the jacket.
I did make additional mods to make this fit me better (the XXS was small for some dimensions but swallowed me in others), but if general flight suit fit isn't a problem it's really almost as simple as chopping the thing in half and adding a closure on the front. You will have fabric that's commonly used by many 501st members and the mandarin collar will already be there for you, top and bottom will match, etc. Oh, and sewing the patches onto mine (with just pants) was MUCH less cumbersome than the same for my husband's (full flight suit).
Happy to grab some pictures later if it helps.