Kupari, a few years ago, we made move that 'felt right' and we love our life here - also back on my home turf.
Having said that, it makes sense to let yourselves grieve for awhile before making major decisions. I also suspect that your older daughter just cannot face any more change after the death of her sister(is this the area she grew up in?)
But it seems you are not rushing things. I would suggest a couple of visits in the next few months - it will distract you from the hip pain, you'll get an idea of what kind of places would suit (whilst struggling with dodgy hip!). You can get a feel for buses, local events etc. We did that a lot.
Then, when you are recovering from your op and sitting a lot, you can do a lot of internet searching (I also did this!).
I would advise against organising a move until you have recovered from your operation - convalescence can be very variable, and you don't want pressure.
I would definitely consider cornergran's idea - you can always rent your own home out to pay the rent on somewhere in Northumberland.It also gives you time to sort out both practical and emotional stuff, so you are sure it is the right decision. It also mens less pressure when you finally organise the move.
Of course you need to be kind and thoughtful to your daughter, SiL, and grandchildren, but you can do this whilst letting them know that this is your life, your decisions. Ours love to come and stay in our house which is efficient and easy to run for 2, but has rooms that can open up for guests.