I'm also a bit top heavy (DD), OP, but I've discovered the joys of the Aah Bra. Not terribly sexy to look at, but they do come in some nice colours and they're amazingly comfortable.
https://www.ahhbra.co.uk/
There are some generic brands around which are cheaper, and I also find them to be really good support.
https://www.ahhbra.co.uk/
There are some generic brands around which are cheaper, and I also find them to be really good support.