Hi yes I'm on that trip and am staying at the Comfort Hotel near Heathrow the night before (I live in London but public transport won't be up and running early enough for the 6am check-in). I booked it through Just You but I don't think it was any cheaper than booking direct.
Hope you enjoy your first solo holiday! I went with Just You to Croatia last September and it was great, so I'm looking forward to this one.
If you decide to stay in the same hotel the night before let me know!
-Marsha