I know the SSR is majorly overated for continous current, but I don't want it to get cooked the first time I try turning the transformer on!

A standard relay is an option, but switching a transformer on is going to provide quite a surge, and still need a reasonably sized relay to handle the surge current.

I know the 3kw 240-415 step-up transformer I use for my 3 phase converter does on occasion trip it's 32A circuit breaker on power up, and that's without any load on it.
The Toroidal is going to be starting under slight load (it'll take a short period to charge the smoothing capacitor), so I want to make sure whatever I use to turn it on isn't going to go up in smoke.