I started wearing Sports singlets with built in crop tops as I did a lot of sport back in the day and also weared then daily to flaten my chest before full transition,
But as they got bigger I started getting fitted for bras by professional bra fitters for a proper comfy fit and love then, my fave are tee shirt bars for a nice smooth look under any top and also it evens breast out if they are slightly different sizes,
But having a sports bra or single is a must if doing any vigerous activity to reduce the risk of bounce or tearing of breast tissue even with tiny boobs,,,,,,,,,,
There are so many options out there its just a matter of finding the right ones to suit your body and the activity you do,
Another thing to remember is sizes will vary with different manufactorers and I found it best to try on before buying............
Cheers Tracy