Hi Jojoe 🙂
Flown with a wheelchair a few times mainly using Virgin and TUI, booking assistance was pretty straightforward but I found the actual quality of assistance depends more on the airports ground staff than the airline.
Some airports are much better at it than others, I found Manchester brilliant but East Midlands quite poor. My local airport (Newcastle) are pretty hit and miss.
Please excuse spelling/typos. Apart from being a clot it turns out I had one on my cerebellum that's now causing various problems!