I finally got this approved by my doctor so I'll share
I'm AMAB nonbinary and taking HRT. My goal is to feminize but without breasts. I just started bicalutamide. In a month I'll start raloxifene. Raloxifene is a SERM - selective estrogen receptor modulator - which acts as estrogen in most tissue but blocks estrogen receptors in breast tissue. This should result in little to no breast growth, while still getting the effects of HRT in other areas like body hair, fat distribution, etc.
You could pair raloxifene with other HRT regimens. I chose bica because of all the anti-androgens it's most likely to preserve function downstairs, and it slightly raises estrogen levels indirectly. At too high of E levels, raloxifene likely wouldn't be able to block all the E. There are other SERMs such as tamoxifen, but raloxifene is safer and more effective at stopping breast growth. I can't post dose information due to forum rules.
Using SERMs for HRT is very uncommon so it's hard to find any info. I only know of a few people on >-bleeped-< and 4chan using raloxifene. It's also hard to find a doctor that will support it - I went to a clinic that has many LGBT services, that does informed consent HRT, and I presented a bunch of information to my doctor to show that it's safe. I'll try to post updates every 6 months.
I hope somebody finds this who needs it. I don't frequent this forum but I'll turn on email notification for this thread and my PMs if anybody needs more info.
EDIT:
I forgot to mention: In the future I may get chest surgery so that I don't have to take raloxifene forever. If you already have breast growth then SERMs may reduce them but surgery is likely needed. I've heard that for very little breast growth (like gyno) there are keyhole surgeries with minimal scarring