Thank you all. I have swallowed my guilt and fraudulent feelings and asked the agent to book me a wheelchair, since it was them who said it was possible. I was expecting DH to say 'no, we'll manage' as is his wont but he didn't - so my limp and slowness must be bad! We went to India a few years ago and the Dubai transfer window was 1 hour 30 minutes and they held the flight for us - and I could jog a bit then!
Although we are on the move a lot and there will be quite a bit of walking, it's a birding and wildlife holiday so being slow won't be a problem at the other end, there's always a distracting bird to slow down the others!
Thanks again all of you for the reassurance that I'm not taking advantage.