I would imagine the reality of such a situation is that once you move in, you will be such a wonderful companion and support to your Mum, and she to you, that you will not want (or be easily able) to leave. Especially as she gets older.
So be very sure you are doing the right thing before you move.
Discuss it all with her before you move.
Decide what you want from the situation : some privacy, the ability to socialise outside the home if you feel like it; how much to pay fairly towards the household and so on.
If you are absolutely sure your Mum's personality and yours are compatible, it will probably work just fine and you can change and refine things later.
Personally, when my Mum moved in with me, prior to finding and buying her own home, it was a disaster.
I was tearing my hair out in the first 2 weeks
but we made it through 6 months and there were sighs of relief all round when we were once more in our own domains.