Appreciate all the advice given. Just to give more info - I am only going to be there from about 8pm until 0540. I have a 0740 flight out of T5 and want to maximise sleep. I don't however feel I can warrant the cost of the Sofitel. And I was also assuming catching a bus at that hour would be a complete faff, if not impossible. Thus my leaning towards the Thistle as the Pods look like a sure fire way of getting there with ease and not at the Sofitel prices.

Loyalty points aren't a deal breaker - for one night hardly seems worth it.

I may have a look at the bus schedule and see what's possible, although this will be in September.