>> And stop overwatering!
Yes, I know that would be a Good Thing. But it's like dieting: the hard part isn't knowing that you should, the hard part is having the discipline.
After years of killing seedlings, I have learned to overwater LESS.
I might try some seedling mixes again some day, maybe I used to buy cheap ones. But every bag I ever bought was finely-powdered peat. Exactly what I don't want any of.