Mornington was a great stay.
Location: around the corner from Earl's Court, which has a direct connection to basically everything including LHR. Lots of restaurants and stores within 1 block. The block that the hotel is on is quiet, with a lot of other hotels as well. Safe. I was hesitant because the hotel is part of the Best Western brand which (at least in the US) is lower quality, but it was actually great and those preconceived notions were proven wrong.
Check-in: easy. Very small elevator, typical to old buildings in Europe.
Room: I had a single room which was just a twin bed and minimal space to move around much, but as I don't hang out in my room this was fine. There was a writing table with stool which was nice to get things organized. A closet rod but no drawers. There is an in-room safe and a coffee pot hidden in a cabinet/drawer thing, as well as an iron/ironing board. Bed was comfortable.
Bathroom: quite small, with a ship-style shower that a person with more girth may not be comfortable in. Shower amenities include soap, shampoo, and shower gel. (NOTE: No conditioner, lotion, nor blow dryer.)
I did not get breakfast, as there are more reasonably priced options within one block, including Paul Patisserie, Pret, etc.