Hi, there are a few alternative meds for diabetic neuropathy which you might be able to have with a bit of juggling of your meds. One is duloxetine, which is also an antidepressant. You'd have to slowly withdraw from the sertraline before starting it, which you may not want to if the sertraline has worked well for your mood, but it's possible it could treat both problems.
Other possibles are gabapentin & pregabalin, not sure if these interact with sertraline or not (would have to check my BNF) though.
These are all for neuropathy, I'm less sure about restless legs, but there are options for this as well (though some are also addictive so may not be the best if your brain is already "programmed" that way). I don't quite know why your GPs haven't suggested any of these so far - there might be some reason in your other meds or past medical history, but it's worth going back with these names to ask I'd have thought.
Hope you get somewhere.