Excuse my ignorance, I have a bit old laptop and I don't know if it would be better
to have Debian 9 so I can, possibly, load KDE on it, or instead Debian 10
but having to limit myself to lightweight applications only.
IMHO: it is better to use the latest Debian even on the old laptop unless your laptop is 15 years old.
It is very lightweight:)
"tasksel" (tool that runs when you install Debian) asks you which DE to enable. You can choose LXDE there.
I run it on my 2011 laptop (sandy bridge) and it works very well.