I'm going to be straight with you. If you have a larger chest and you're not naturally shaped nicely enough that you can go out without a bra, I wouldn't recommend it. In hindsight I should have gotten one of the sports style bras instead (but I had dreams of wearing cute singlets with thin straps).
I wear a size 16D in bras normally (size 12 for dresses, 68kg at 164cm. 41inch bust, 34inch directly underneath where the band is), and bought an XL. If you're my size you know that for a normal bra, the straps start to get pretty thick for us. The band size I picked fit me well and the cups had good coverage, but it really doesn't give much support-- which was expected from something with straps this thin, but unfortunately it's also very unflattering on me. My chest gets squished in by the fabric, but the band doesn't do much for stopping the sag, and because it isn't very supportive, my breasts splay outwards.
I think it's a good product, but not for all sizes and shapes. The original plan was to take this bra on a backpacking trip, but unfortunately it isn't something I can wear outside the house since you can see the shape of my chest isn't quite right even underneath a t-shirt. But I'm a fan of the materials and it is very comfortable, so I'll wear it around my home. If you have a larger chest and some sag, I'd give one of the less cute but more supportive looking sports type bras a shot instead. Fingers crossed that ioMerino gets into physical stores one day so that we'd have the option to try them on -- bras are hard to buy blind for sure.
