Chess Variant Idea (pieces with a health bar)

if the king has 39 health then it's gonna be impossible to checkmate or kill the king given your principles

like you can take any piece and boom the king has enough health to survive the rest of the game no matter what

not true, because for example if your opponent only has a king left, and you have other pieces, those pieces can regenerate to obtain enough health to kill the king. If the combined max health of your pieces is still smaller than the opponent's king's health, then you can just send the health from your pieces to your king

i take that back. If the combined max health of your pieces if less than the health of the opponents king, then it's not possible to win by my current rules (unless you can somehow force the opponent's king close to your king and capture it). Maybe there should be a rule that a lone king takes one health damage each turn, or something.

Not quite what you're describing, but Nichess fits your idea of pieces having health points. Take a look at https://www.nichess.org/