As a paid subscriber to Say Chess, you can now download Blindfold Chess Problems from this post, featuring 1160 blindfold mate-in-two problems.
I have spent some time organizing them, so the difficulty gradually goes up. The first 25 problems have only 3 pieces to visualize. The hardest problems in the book have 7 pieces to keep track of and will be quite a challenge for most.
If you find the first page too difficult, the book might be a bit too demanding—just a heads-up! When that is said I think it is fine to invest extra time on each of these problems in order to solve them.
Take your time, and enjoy the challenge!