I had found one thing that helps me and I have had ingrown toenails for ever. My toe nails that ingrow are very thick. I file down the face of the nail at the corners. I use an emery board to do this. I make it pretty thin. Also not letting the nails grow long helps too. I know the cotton under the toenail trick. It does work. I like my way better.
I agree with you on trimming them straight. Cutting off the corners helps the pain at the moment but more suffering will happen when the nails grows more.
Take a look at the nails at the web site below. Mine do not grow this bad, do yours ?