Don't forget that you don't need any bundlers and frameworks if you just want some reactivity, React is very minimal and works in pure JS, just alias createElement to something like el() and off you go
I'm not quite sure I'd go as far as calling React minimal, but yeah, there are definitely fairly light options here. Mithril is pretty classic as a "bare minimum framework" option. Vue can be used without any bundling/compilation steps as well, although I think that's less supported these days. I also quite like SolidJS - again, they encourage you to use the compiler, but you can also just use it with template literal strings and it should work just fine.