It's a difficult one mate. I went down the nats route post raf. Had a basic course and aerodrome course and then posted to a unit. Wasn't happy with where I went so applied to a non nats airfield.
Luckily got accepted as a tower only controller and the company then sent me on approach radar course 6 months later. Now fully valid and deputy supervisor 8 years later so it's certainly achievable.
Most airfields are unlikely to recruit someone without any ratings though so it looks like you will need to find some way to fund it yourself unfortunately. For what it's worth there will be plenty of jobs out there. Aging population of atcos and all.
Good luck. Pm if I can help in any way.