After wet sanding and polishing a few years back I went with a custom cut headlamp protection kit sold by XPEL:
XPEL Head Light Protection

Not the cheapest product at $70 but it does last. They guarantee it against yellowing, cracking, peeling, etc., for 7 years. Once you've restored your headlamps, the installation of the film is relatively easy because the pieces are small when compared to trying to cover a bumper or other complicated shape which often makes sense to have a professional install. But the headlamp/fog lamp kit is easy enough that just about anyone can do after carefully reading the instructions. It is a little disconcerting when first applied because the film is applied wet (solution of rubbing alcohol and water) and some of that liquid will get trapped under the film leaving the lenses foggy looking. But almost magically after a few days it all evaporates leaving a crystal clear headlamp.