Fancy gas isn't essential for indoors it's all about technique.
I've only had one joint leak, done up to 28mm no trouble. Used whatever torch
wickes sold cheapest. Try to do as many connections as you can on the bench, then do the final ones under the floor.
The prep is important and for bigger joints always heat all around the fitting not just one side. No need to heat the pipe, and the solder in the fitting should be plenty.
You need very little flux but the pipe and fitting must be clean.
I tend on large fittings to heat the bottom of the fitting more at first then switch to the top once it melts.
For bigger fittings I turn the gas down to give me more time to warm it up.
All a case of it works for me, but you just need practice u until you can do it reliably.
I've had a few good tips off members here so hope I can pass it on.
Edit was I pressed post too early, sorry