You haven't mentioned a budget, so I apologize if this is not accessible to you. Also, I've always been pretty thin and am blessed with a somewhat androgynous figure to begin with, but I'd rather share what's worked for me than outright assume it's not going to help anyone.

Totally depends on your personal tastes and comfort levels. I got some cute crop tops on sale for under $10 from Uniqlo a little while ago that I love, but it's definitely also a little scary to start wearing crop tops in public. I also got some (unisex) parachute cargo pants from there that are pretty trendy and absolutely great for transfems because it makes you look like you have hips. I've gotten a lot of compliments.

As a fairly tall girl (6'2), I've had some luck finding jeans that fit me nicely from Madewell, they have good size options but they are a bit pricier, but a decent option to try if you can afford it.

As for underwear, I've tried a few different brands but the only thing that I've found to be fairly comfy and *ahem* accommodating to my anatomy has been aerie boybriefs, specifically the cotton with elastic bands. Sometimes they sell 10 for $35 or something like that.