Hi, @neveradullmoment99.
I ordered a Medium in both dresses. I am a high street 12 irl - small shoulders and frame but with a large bust!
I found the gingham roomier on the bust than the sail stripe, but with slightly less material in the (very) full, swishy skirt.
For me, they are tts on top. Those with small busts and shoulders might prefer to size down.
I am still sad I had to return both as they fitted me well. However, the gingham triggered migraines, (I am hyper-sensitive to some patterns), and I wasn’t keen on the noticeable seam down the middle of the sail. Lovely colours and fit, though!