My dad is 81 and started having hearing loss a few years ago. He just sent me a pic showing the degree to which he was able to shrink his DIY hearing aid once he settled on the circuit design:
https://photos.app.goo.gl/4lOwfrVJ3bfRWkEm1
(Stereo mics and amp with two-channel parametric EQ on each side. About 6" wide and runs on two 9v batteries, if you're curious!)
He took it to a Bose showroom to compare it to their Hearphones. All (Bose people included) agreed that his amp and EQ was superior. Cost for parts is ~$200. He's had a lot of fun building them for himself and his friends.