If I need an overnight stay prior to departing from T5 I always stay at the Premier Inn at T5.

I can usually get a room for £69 and sometimes as cheaply as £40; the 423 bus stops to & from T5 are literally outside the front door of the hotel.

The rooms are clean, the bed comfortable, the restaurant is pleasant and whilst not fine dining, the food is perfectly satisfactory and usually better than what you will get served on the plane the following day….