Both windings will be getting used in series or parallel, depending on which tx I get.
I'm going to get a switched mode Din rail 12V PSU for 12V needs to simply things, so don't need any extra windings.

35V is cutting it a bit close. It theoretically gives 49.5V rectified, less 1.4V for the bridge, gives about 48V, but that's at a rated input of 230Vac, so by the time you allow 10% for mains variation, it takes you well over 50V.

Think I'll go up one size at the same time (existing TX was 160VA), to allow for future additions, so will probably go for a 225VA.
Airlink is the cheapest supplier I've found, but need to check on postage, as I need other bits they don't do.