i just wear a strapless bra! mine is from victoria secret (not sure the exact style name since i got it years ago) but tbh it’s not the best fitting IMO (has a lot of space if you’re flat like me lol). i haven’t tried a strapless from skims but i have their regular bras / bralettes & they are my favorites - specifically the fits everybody ones & the naked collection for bralettes. i know you specifically asked about strapless / sleeveless items, but the naked collection bralettes from skims are great for a seamless look under really tight basics like the long sleeve basic top i showed in this video.
just tested it by trying it on with a black bra under and you could see it.. it wasn’t super sheer (it was fine with a nude bra under) but if you choose to wear nothing under or pasties i think it would show through! hope that helps :)
