In terms of optimization, Gentoo is the best you’re gonna get, but the word “convenience” makes me hesitant to recommend it to you.
Arch is minimal, and has many resources/guides on battery optimization (Especially for ThinkPads), but if you’d like to learn something else, Void is the way to go.
If you’re looking for a tiling WM, I can wholeheartedly recommend bspwm. Lots of control and customization, but pretty easy to configure when you understand it. Just know, it might be a hard change going from stacking to tiling.