Shirts that have a gap between the boobs.

[aboywithgirls]

Lane Bryant might be a good place to start. They have plain button down shirts in white, black, light blue and a number of other colors and patterns. Also check out Exclusively Kristen. I have a couple of their tops. They are very good quality and look good too. They are also very "accommodating ".

[dr.moe]

Another option if you can follow directions, are patient, and can think logically would be to make your shirts.  Yeah, I know it sounds scary.  In reality, it's not (with a bit of practice).  First thing I made was a shirt, then tux and accessories for my wedding.  (Details aren't important unless you want to PM me to relieve your boredom!).  If you have someone who can help tutor you, all the better.  You don't need a fancy multi-hundred-$$$ sewing machine either - my first machine was purchased for $8.95 from a thrift store and could only do straight stitches.

I've made dozens of shirts, pants, and jackets for me, and blouses, skirts, and women's suits for my wife, plus a couple of suits for me.  The best part is that they're very-well-fitted.  For darts, my wife thinks that's the best part. The apex of her bust and her dart size aren't standard, so fitting them is much better with custom-tailored.  For me, the way my body is shaped, I have to take in a lot anyway to make a shirt fit halfway decently, so I come out ahead. YMMV.

If you're retired, or have free time and need a hobby, or just want to feel creative, it's not a bad hobby.  It's not as cheap as the $9.95 Amazon-imported-specials, but you know the quality of the material and sewing, and generally, shirts will last a LOT longer.