I would be honest & upfront about your situation. A good, professional escort will take your personal circumstance in to consideration and accommodate for it. You definitely want the 'GFE' e.g. girlfriend experience, avoid the PSE/pornstar experience. Just find a girl who understands you might need to take it slow & possibly the odd break if you get exhausted, I would say either start with a one hour booking so not to knacker yourself out or book a longer booking .e.g 2 hours so you can take your time.
Good luck, you'll get back in to the swing of it! x