Hi,
we are also in our fourty‘s and we don‘t like shows, dancing and entertainment. We love quit ships… so we prefer going with the small ships of holland America. Two years ago we had our first cruise with O and it is more quiet then we knew it from HAL.
So O is definatly the wrong choice for you.
There might be solo travelers on O, but they will be much older then you.
In October the Mediterranean won’t be that warm any more. We always go in the beginning of October. But you also might have some rain.
On the Canary Islands you will have the better weather in this time of year (normally).
Palma de Mallorca and Ibiza are nice ports for cruise ships, also Funchal on Madeira is great.
Have a nice trip to Europe