Mint 19.3 is still supported and pretty good. You've got about 2 years to save up for a S/H 64 bit laptop.
I've 64 bit, Mint 20.1, but I won't update to 20.3. I'll see what the next LTS in the 21.x series is like.
Still on Calibre 5.44 here
A laptop needs to be terrible not to manage Mint desktop. But XFCE is certainly less hungry. I usually install Cinamon and XFCE after Mint, and an extra user or two in case I break something.