i don't think my preferences line up with what you're after, so maybe ignore this. . . .
i'd recommend explaining computers youtube and website for beginners - he'll give you much better advice than me https://yewtu.be/channel/UCbiGcwDWZjz05njNPrJU7jA
but FWIW i reckon mint+xfce. will give you "easy" and "decent performance on old hardware"
you can try out the more flashy d.e s on a usb boot drive see if you think the features are worth it on your setup.
always remember it's easy and cheap to experiment.
get yourself a system for backing up your "home" directory, - a couple usb drives is easy enough.
and i'd also recommend starting a text file list of all programs/packages you like to install.
you can make it into a bash "sudo apt get " script (for debian based) if you're feeling super lazy.
, or just run through it manually whenever you switch.
also do the SSD upgrade as soon as you can afford it, it'll make everything a lot better