I am sorry that you feel that you cannot live with your son.
The point is that you are the adult and you have the choices here.
If you feel you cannot be a parent to your son you should allow your mother to be his carer. If that means you move out that is what you should do.
As a single woman with a good job you will be able to find a rental property.
Your mother can claim CB and CTC/WTC for your son as his main carer.She will be able to apply for a Special Guardianship Order so she has PR for him.
Your son will remain in his home with someone he knows. The loss of his mother will affect him but at least he will have some consistancy.
As your mother has already said she will have him, adoption is not in his best interests, or yours. Even if it feels that way.
You may feel that if he is adopted you can have a fresh start. It really is not as simple as that. Adoption means forever. You will lose all legal rights to have contact with your child. You will no longer be his mother.
As has already been stated - you son will not go from your home into a new adoptive home. He is likely to spend time in foster care and there is no gaurentee that he will be adopted. You really need to take note of this.
If your mother tells SS that she wants to keep your son SS will be unwilling to get involved.
It may be that you are suffering from depression. It does seem that way to me. I feel sad that you are feeling this and want to take such extreme measures.
Others have mentioned that you seem to be focussing on your son as the root of your difficulties. It sounds like that to me too. This makes me think that you could do with some help in working out what is going on. If you need to move away to do this then do it.
Your son will be well over 4 before he is anywhere near being adopted.
This means that his chances of being adopted are low.
If you say you do not want to care for him I belive you (and I am not judging you because I dont know why you feel like this) but do you really want your son to spend his life in care?
I really urge you to get some help. I hope you find a way through this.
Your son is the most important person in this situation.