I have the same thing, but in reverse, and it's interesting that you highlight mannequins. Town centres are the toughest place I can be precisely because I'm envying them all. It's dysphoria central in those shop windows, and it's that which made me realise I really had a problem.
There are some ways to dress around physical shapes. It is harder for men, because while women have access to so many different styles of clothes, there's also a lot of advice out there for X, Y and Z body types. I hope you'll forgive my comparison, but there are some (cis)men who have to dress around so-called 'man-boobs'. Loose t-shirts or vests and the layering of a jacket or waistcoat can help to flatten your body, and binding would probably help you out too. Not that either of those options is a comfortable one now that we're in summer - I'm kicking myself for trying to transition now, as corsetry, chest and possible hip padding are going to leave me half-dead in this heat!