It might be worth doing a module or two at the OU, which shouldn't affect your eligibility for funding for a full time course (check with SFE first though, just in case; also it may affect funding for part time), will refresh your academic skills, and you can then ask the course leader or an individual tutor to provide an academic reference for you? This would probably tick every box, and can be done part time while working (and can help you explore your subject a little more from the academic angle before starting formally).
Otherwise, I would probably suggest outlining your situation with the institutions you plan to apply to and see what they suggest; a client would probably not suffice, although a work colleague might.