[Measurement Check] [Recommendations] I think I measured myself to be 26DD but the calculator said that doesn't exist?

I think 28D is a good starting point. Bratabase browse by size -> measurements tool is a really useful thing. Here are 28D sorted by how far the bra bands stretch. As you see a number of them stretch to less than 28", I think around 27" to 28" would be the sweet spot for you but you could go a touch looser too. You don't have very heavy breasts so you do not necessarily need a very snug band, you have a little bit more leeway.

Skarlett Blue seems to have true to size 28 band bras and shapes that look good for smaller breasts. They have two bras in 28D, a touch pricy, but free shipping and returns for purchases over $50. I just found that they are also on Amazon.

/r/ABraThatFits Thread