I have Iphone 12 pro max and am in similar siuation. It depends if you are happy with the quality of the pictures from your current cameras. I’d say that is the biggest upgrade (better cameras). You will get USB-C on the new phone so won’t work with your old cables (so much for saving on landfill).
If the battery is getting old - you can get it changed for a new battery for a couple hundred pounds at the Istore - a lot less than a new phone.
Iphone 12 runs the latest software so no difference in content.