The FT QL was my first Canon SLR way back in the 1960's. One of the issues with the old cameras that used 1.3v mercury batteries that are no longer available. I buy and sell a lot of the old cameras.
You can use either FL or FD lenses with the camera, there are tons of 50mm f/1.8 lenses available for under $50, and f/1.4 lenses don't break the bank.
There are few good alternatives, Silver Oxide works ok, but the voltage fluctuations mean potentially inaccurate light meter readings. Air-Cell batteries are expensive and don't last long.
A separate light meter is the best solution.
Its also pretty likely that the shutter speed is no longer accurate, its impractical to do anything about that, just try it and see.