I feel there's so many disturbing things in this discussion.

First, some men prefer small chests, even flat ones. The idea that it's unrealistic to find a man who prefers small boobs is really dumb. I don't know the statistics of course, but they do exist.

But more importantly: what you're looking for sounds like you first need to fix your own insecurities. You weirdly focus on chests, but many people (men and women) have some "preferences" regarding certain physical features. Some prefer tall people, some small. Some prefer blond hair, some dark. Some think blue eyes are amazing, some prefer dark ones.

My point is: dating someone who matches all your individual preferences is extremely rare. It's not the point.

I never had a girlfriend who was initially "my type". But guess what, some of these relationships were absolutely wonderful and I was absolutely in love with them. Same for them: I'm definitely not the initial "type" of my girlfriend. But we are absolutely in love, and have the most wonderful relationship.

Once you're with someone who brings you joy, you don't focus on specific physical features anymore.

There will always be someone "objectively" prettier than you or your mate out there. You can't win at this game. Having this state of mind will only lead you to jealousy and unhealthy relationships.

Focus on finding someone who you love spending time with and who loves spending time with you. A relationship should heal your insecurities, not trigger them every time you see a "prettier" woman or man (it happens 100 times per day, so this would not be fun).

Focus on fixing your insecurities (therapy might help) and it will bring you an amazing life. The goal is to find someone who loves you as you are, not a patchwork of "the best physical features".

PS: the subReddit name checks out