Hi Ali,
For me, searching for appropriate underwear, bras, and bathing suits (that support both belly and bust), has always been difficult. I've had my ostomy for over 50+ years....and although I don't like having anything "tight" around my waist, I've always worn a light support/stretch panty. That's mostly because I was "inflated" with fluids (from steroids) when I had my surgery, and then after it, I had to wear a back brace....for almost a year. (Degenerative Disc disease/Osteoporosis). After the surgery, and off the medications, I lost all the water weight, but found that the skin on both my belly and "boobs" lost elasticity and texture. No more did I have a flat teen/belly. But the elastic panty served me well, even though they were often too high. It took me into my 20's to spend the extra money to have the undies cut down, and a lighter elastic put in. When I find panties that "fit," I buy a dozen...or more. I tried the high leg, Jockey stretch....but they were way too light to hold in both my belly and to keep my pouch in place. Years ago, I found a style in one of the plus-sized stores that really worked well because the waist was low, didn't bind or irritate, but kept the pouch firmly against my belly. They still make the same style.....so I buy another dozen every few years. In the past, when a bathing suit material was too thin, I wore a pair of panties under it....just to be safe. But these days, many suits come with that control belly panel....which serves the purpose. At night, I just wear a cotton brief to keep my pouch in place, in case I try to roll over. Haven't slept on my belly for 50+ years. I hope this helps... Kudos to you...Vikinga.. I have never worn a string bikini, much less string bikini underwear.... Sigh... I didn't have the figure for it when I was 12 (and got sick) and after surgery.....I was a lumpy bumpy mess. But no real regrets....because I'm alive.. These are just "shopping" challenges.