Bear in mind if you work 16+ hours a week you will also get to keep whatever your ex is due to may in child mainetance. If you are on benefits you don't get to see much if any of it! However this may then affect your Council tax and housing benefit.
I work 18 hours a week, at above mimimum wage rates and am very lucky to have a good employer who is very flexible with my hours as long as i get my work done. However i have high travel and parking costs and get very little support from family. I am broke most of the time, but I am much better off than i would be on benefits and can now afford to run a car, which i need so i can travel to work, but also because i live in a rural location and it's the only way to get to shops etc. However i do not have money to buy clothes, makeup, get my haircut once a year, very rarely go out and can never afford to have friends over for a meal.
I choose to spend the little extra money I have on activities for my son and doing things at the weekends. My son's clothes are mostly supplied by his paternal grandmother and i am very grateful to her for that. There are still some weeks where money for food is scarse and i have to not eat to get by. Fruit and veg is a luxury in our house and we eat a very limited diet, mostly pasta as it's cheap and filling!
I keep to a very strict budget. I have calculated my annual bills for everything and have a max of £40 a week for shopping for the two of us including toiletries and cleaning products. I put money into a seperate bank account each month to cover the bills (electric, council tax, water, phone..), child care, car expenses, and i put a bit aside each month for xmas. When the bills come in i then have the money to pay for them and when the car needs its service or road tax etc i know i have the money there. You have to be very disciplined and not take the money to pay for clothes or school shoes etc as you need it for those bills. I often moan i have no money for things, yet i have money in my savings for the bills. You have to regard it as seperate money and not be tempted to take it when you have nothing for food! I know i can not afford to take that money for other things because if i allow myself to get into debt i will never be able to get myself out of it and i can't afford to pay for loans or overdrafts.
Being a single parent is not easy. But working now means i can afford to heat our house and run a car and my son has swimming lessons now. On benefits i could not afford to do those things and in the winter we had to sleep in one room just to keep warm and i regularly had to go without food. Now it's much better but still not as I would want or like or choose to live.
Get as much advice as you can, work out your budgets and be realistic about what bills cost and what you can afford to go without. Be prepared to have to tighten your belt and go without and expect your ex to cause a fuss about paying towards the children. If you're the kind of person who can't live without your tanning bed sessions, getting your nails done and likes to shop and go out at weekends and enjoys takeaways and eating out then you will find it very hard to get by. Think about what is really important for you and the children though. I wouldn't advocate staying in a relationship you are unhappy in and is not working, but i wouldn't want anyone thinking being a single parent is easy.
Best of luck with whatever you decide to do.
Gilly