I think you are the first time to book an apartment through website.
I would like to remind you that you can book such apartment over 28 nights if you concern your travel insurance is not cover. The host will issue you an official tenancy agreement.
Regarding the noise from downstairs.
My apartment is beside the "Ladies Market". Obviously, it has some noise from the stalls during they are taken down and put up. I think it is not a problem if you shut all the windows and switch on the air-con during you sleep. I have been stayed there overnight but I did not find it was noisy. I think you love silent as your home in UK.
Anyway, thank you for your review!
Hope to have your booking for my other apartment on coming future!