As a lot of people have said, there's nothing wrong with moving in with your mum and from your answers to this thread it seems like you are putting up barriers to other suggestions and wanting to do this. But reading your first post very carefully, I would think very carefully if you are really going to go down this line.
You say it would mean moving away from where there is more people and to a much more isolated place. You say it's two hours from your work and friends. You say you are an introvert. You say you would like a relationship maybe in the future? You say you have got depressed in the past when you lived on your own.
As others have said you do sound quite anxious and avoidant. I'm very sympathetic to this. I can be the same. But the idea of moving somewhere isolated with no going into work, no access to friends and no opportunity to meet new people, so that you can move back home, does strike me as putting all your eggs into one basket. Your mum will basically be your social life. It's really lovely you are close and that she's so supportive of you. But what will motivate you to make those social contacts which as a person who does get lonely, will stop you feeling this?
You are adament against renting out. But what you don't answer is about the suggestions of not working from home. So many people make social contacts through their work and it can be more natural that you make friends this way as it isn't something you have to force yourself to do, like going out for an activity.
Is working from home something imposed by your work or is it your choice? If it's your choice I might have a serious think about whether you are withdrawing slightly maybe through anxiety. If this is the case, it's really worth trying to counteract earlier rather than go into it further as you could end up with your world getting smaller, which isn't good for mental health.
I wonder if another approach might be an idea. What about suspending the decision for a year and thinking for this year you're going to try something and go into a much larger flatshare. I have done this before when I moved to a new area. It's not the way I wanted to live permanently but for a temporary period of time it was good and provided a base and company. If you think you are doing something for a temporary time you don't have to feel trapped or stressed. A bit like doing a course for a while. In fact a flatshare with mature students or something like that might be ideal as it's a set of people who also will be wanting to get some work done. I'd also look into working in the office for this time or, as others have suggested, maybe looking into hotdesking or shared workplaces to have a routine, get out the house and make some low social level contacts and interactions, which is supposed to be very good for us all.
I'd also look into trying some evening classes in something that really interested me to broaden out interests, learn a bit and make a few social contacts hopefully in subjects that interested me.
At the end of the year I'd review the situation.
The danger of moving back in with your mother is, as you outline, it will be a lot harder and you will have a lot less motivation to create new social contacts or maintain old ones due to distance. You won't have access to classes or interest groups as she lives in a much more isolated place which is 2 hrs from those things. You will also be committing yourself to working from home I presume, as it is far from other jobs, places of work where you can go in.
The option of moving in with her in the future remains if you want to, so you're not burning any bridges by trying a different approach for a bit. I would definitely look at the working not from home if you can as a first step and as a flatshare is one of your options, I'd go for that, but with maybe a few flatmates rather than just one, for a year. Good luck whatever you decide OP!