What matters most when choosing senior living?

Checking all the financial aspects of it. Extra costs, large increases in maintenance, any other restrictions on the use of the flat (no overnight visitors) and remember that when these flats are sold they developer will a cut of the sales proceeds.

That is assuming you can sell the flat because these flats often sell for less, much, much less than the first resident paid for them and maintenance charges, which can be £1,000 a month or more continue until the flat is sold.

In fact if you go ahead, do not buy a new flat directly from the developer but look at those available on the resale market and check that when your mother dies, if the flat is slow selling you can rent it out, providing the age of the tenant, complies with the leasehold rules.

Re choosing a community, access to other amenities - shop, PO, chemist, GP and so on, bearing in mind increasing frailty over the years. Size of flat and outlook.

Location. Easy for family and friends to visit. Some may want to use public transport, others will want easy parking
Proximity to shops, library, GP etc etc.
Pleasant green flat walking area.
Flexible meal times. Likewise use of
washing machines if shared
Heating which can be adjusted to suit. Some places are too hot!
Ratio of staff to residents
Storage space.
Activities and regular outings
Somewhere to entertain visitors.
A room for overnight visitor