Should we move to the USA?

Unless money isn't an issue I would look carefully at the healthcare costs on your next visit. Make it a fact-finding trip. See if your son would have to sponsor you and what your status would be there.

I know there is an ex-pat community in LA - speak to them as after all they have done this.

My son in his 30s now pays $900+ a month for partial health insurance. It's the best he can get apparently. He's no longer in California (which may or may not be cheaper/have different rules). He was happy there and loved the lifestyle. He lived near one of the beaches and his flat therefore was very expensive. Have a look around the areas you like and get a feel for prices. Don't rush into it.

Can you rent your own home out for a year here, and rent in LA to "try it out"? You could put precious items in store.
I'm sure that would make things clearer.

Good luck.
We lived in America for a year or so when we had a young family. Lots of things were considerably easier than here and lots of things we missed. The thing I suppose we missed most was the shared heritage. I wouldn't have really put my finger on that then, but you can speak the same language and make great friends (as we did) but you still come from a different mindset, a different place.
Sometimes we need to open up to change though - so certainly not all bad!

That was my first thought too Bossyrossy

What about buying/renting a small house or apartment near your son and spend six moths there and six months here? It might help you make an informed decision about your future without burning your boats in the U.K.