Childcare costs and work! Confused and dont know what to do!

Hello,

I am after a bit of advice about working, childcare and benefits we get or dont get etc. 

I have a lovely baby boy 8 months old. I am currently still on maternity leave but need to make a decision soon. My partner and I are living together but not married. We have a mortage to pay as well as his car on finance. I work at a school as a teaching assistant and earn just over £900 a month(full time). He works and earns around 1200 a month(full time). He pays for mortage payments and his car payments. I pay for gas/electric, tv licence, council tax and water. I mostly pay as well for food shopping. However he does help with this.

I have been looking into childcare options. Yes i wasnt very organised like a lot of people. I wanted my son to go to a childminder. So i found out only to find out it would cost me during holidays as well. Something we cant afford. So contact local nurseries some who do just term time places. I then thought about going back part time maybe starting with 2 days a week. My mum has offered to have my son one a day a week but she also works. So i could go back 3 days 2 days in childcare and 1 with his Granny. However my partner thinks it would be best if I go back full time. When calculating this it would cost around £200 a week in childcare, so therefore would leave me with about £100 before bills. The bills each month come to more than £100. 

We are applying for univeral tax credits but would we still be able to claim if we work full time. I have look into changing my job and working weekends or evenings but my partner works on a farm and therefore has major overtime in the summer months and around xmas. I really cant afford to go back full time but would like to go back part time but have no idea of its going to be cost affective. 

Does anyone has any suggestions about what I do?