go for the 28mm units, for thermal insualtion the pvc windows are best in my honest opinion as ali windows still get cold spots. Company’s try to flaunt the “argon Filled” as a sales pitch but its pretty standard these days every unit i fit has the stuff in it…
depending what company you go with will depend on the quality of the windows/locks they use. ask them to tell you the name of the system if its duraflex just avoid it. its cheap and nasty stuff. Rehau and system 10 are better quality as are plenty others.
With doors as above state the Composite doors now outclass any pvc/timber door they are brilliantly secure and look brilliant for a very long time.
Recently fitted a whole block of flats for local council with composite doors and there was a police raid on a property there. They spent over 45 minutes trying to get into 1 of the doors we had fitted then gave up and smashed through a side window instead was very funny to watch them :lol: