Last couple of trips to T5, we have stayed at T4 in the new premier inn which is attached to T4 by the same walkway used for the T4 Hilton Hotel. We’ve booked again for later this year and the room was only £29.50 and while not as luxurious as our stays at the Sofitel the premier inn is a decent hotel.
I did see see there is some new Holiday inn & Crowne Plaza opening in the same area of T4 so might be worth a look if you are happy to travel between terminals.
Weve then got the free train transfer from T4 to T5.