I highly doubt you need to replace your arm, just the bush. I’m about to do mine, common problem, I’d personally polybush both sides, I use the Hardrace rear trailing arm bushes, they’re around £70! You can get them on eBay, 6two1, tegiwa etc
I’ve never done it or know anyone who has but I imagine it’s more hassle than it’s worth tbh, the wiring alone, I bet all the interior loom is different! You’ll have to fit a clutch pedal and everything else, it’ll be easier to just buy a manual car.