Hi Paa
Sorry for your problems, which being honest I have no real knowledge of but the following is offered in case it might help re bra and sternum.
Having tried front opening longline bras in my early days as a fully sidned up member of the "brotherly bra society". I have to say that I found them very uncomfortable after minimal wearing - even ones with a single closure and the more closures the more tricky to close and guide breast tissue at the same time.
I wondered whether in the US they have what we in the UK term High apex bras. These are very supportive and are available with and without wires and with various thickness bands and numbers of closures and either formed or very soft but shaped cups.
Below is a link to a type I wear made by Marks and Spencer.
The bad news (??) is they usually have a fair bit of lace. The one in the link which is typical of many has very soft cups with minimal comfort padding . Laterally the curved, shaped bands of solid material (not stretch) together with underwire cup the breast gently and support without pushing up. Most of these bras are dcescribed as increasing cleavage but they seem to achieve it without noticeably increasing projection which I know you are not keen on. I don't flaunt what I have got, but usually do wear styles that increase projection a bit.
Hi apex are my "go to bras" when wanting to be deliberately discrete .I like them so much I bought 3!
You may find something similar and will at least give control and keep your sternum more comfortable
The metal at the gore of the bra is just an adornment/branding that can be snipped off!
I hope this helps or a least stimulates thought - if not, forget it
Best Wishes
Make sure you paste the following as one complete entry No gaps
https://www.ebay.co.uk/itm/MARKS-SPENCER-M-S-AUTOGRAPH-HIGH-APEX-PLUNGE-PURPLE-SILK-LACE-BRA-32-34-A-B/132598946971?hash=item1edf835c9b:g:kAoAAOSwaZFa4eGE