Being lightweight or not doesn’t depend on the distro but the desktop manager (the graphic interface). Unlike Windows, the graphic in Linux is separated from the system so you can use different desktop managers on the same distros.
The lightest DE is LXQT but it’s pretty barebone, XFCE has more features while still being very light, avoid GNOME and KDE.
That being said, I suggest you try Linux MX XFCE or Mint XFCE first, if that’s not light enough for your liking, try Lubuntu, that’s Ubuntu with LXQT as default DE.