Ive got a 4.1m Frewza aluminium pontoon boat. Boat plus motor etc weighs about 460 kgs. I launch solo, and Im similar age (71).
If theres not a jetty, I have to leave the boat beached while I get the trailer. In a harbour that's usually ok, as any waves are usually very minor, and the boat doesn't get pushed sideways. Where I am at present - Whangaparaoa - Gulf harbour is fine with a jetty, plus a breakwater; but, sometimes I want to launch at Tindalls Bay with no jetty and no breakwater - often waves push the boat sideways, and when I return, its up on the sand. I have much difficulty pulling it off, as my back is not good.
Second problem - waves can make it hard to manoeuvre the boat straight behind the trailer. But that's going to be same with or without a jetty - more due to lack of shelter from the sea from a breakwater or other shore feature.
Thinking about it, for that reason, I wouldn't tolerate a regular beach launch outside a sheltered harbour. And - a solo launch in a place exposed to waves,
Another thought - without a jetty, I think the 4.1m aluminium boat weight is about the maximum that I can handle, solo launching and retrieving. A 5m aluminium boat would be too big I think. A fibre glass boat would be far too heavy.
These problems would go away if a have someone else with me, but find it hard to arrange normally.
You say moving, possibly northern BOP or Coromandel. Only place I do know, Whangamata - has a good all-tide beach launch, in harbour sheltered from sea waves; a jetty. And the access in and out of harbour appears to be ok in all tides. I don't think I would have difficulty with a bigger boat there. Nice for us solo operators.