I finally finished the current content and I love your game so far, gg ! (Sorry for my bad english, I'm french)
I don't really know what you could add or change anymore, since everything I want seems to already have been said in the comments, maybe except adding new possible upgrades when you slept 1000/1000 (yeah, I did it), as easter-eggs or as real upgrades. Make them useful, but not extremely OP as well, so that don't break the game but still make it easier. (For example, a global speed multiplier for the previous multipliers, based on the maximum power reached, and the speed multiplier would be : 1 + (x (maximum power reached)/1 million (what you need to beat the game); I hope you like the idea, but do it as you feel it.)
Good continuation for the rest !