I’m thinking of switching my thumb keys (currently space and enter and two of them go to a symbols layer) to shift. I find that shift makes me anxious when typing because i have to partially leave the home row, and as a result my pinky placement when typing is bad, my ring finger tends to take over and my pinky has become a mod presser and not a typing finger.
I have tried to overload the home row keys as modifiers but that is a huge mistake as it causes misfires or takes TOO LONG to aviate, there is no middle ground with that one.
A lot of people use Miryoku to type fast and accurately. There are settings to fix/alleviate this if you are interested in going down that path.
If you are using QMK setting the TAPPING_TERM low (200 or less?) and enabling IGNORE_MOD_TAP_INTERRUPT will help a lot I think.
I use miryoku and typing uppercase is annoying. You are either swapping shift keys as you type or you have to use caps lock (ewww). Let me know if there is a secret.
Caps Word might be the secret you are looking for. It’s invaluable for writing constants when programming for example.