Hi Mark
£300 for trade-in is quite a good price. A couple of years ago, I sold all of my Nikon DSLR gear and went over to mirrorless at Olympus. Last year I upgraded this to a S/H Olympus EM1 Mark II which only had 1000 clicks on it.
https://www.imaging-resource.com/PRO...conclusion.htm
What I like about the Olympus is how it is weatherproof, small and light, with 2 memory cards.
Personally, I find buying a new camera to be a very stressful affair, as there are so many on the market with advanced technology and features, then there is the decision whether to go full frame or not
All the best
Phil