If you can get into a bedsit, you can apply for HB and have it paid directly to you, then you pay the landlord. The landlord need never know. It means saving up a little to get in there, but takes away the pressure of finding the rent every single week.
If your current job is not enabling you to live - find a different one. Are you looking? (I know we don't live in a world where you can pick and choose, but many people do find jobs every day.)
If the area is too expensive - move to a different area.
The most unhelpful thing a person can do in a bad situation is to close their mind, to say that they have no choice. There are always options. They may not be ideal, but most choices are not...
1 - really great option, fab life, total happiness
2 - shitty option, pain and suffering, misery
How great and easy would life be if our choices were like that? ooh, shall I go for happiness or a big pile of shit - hmmmm let me think....
Sadly, more often than not, it is shitty choice number 1 v shitty choice number 2.
But you do have choices. You just don't have easy choices. But you have to do something, are you still going to be coming on here in 20 years, moaning about life with your mum and her husband, but listing all the reasons why you can't do anything about it?