Don't forget housing benefit if you are renting. If you need somewhere to live you need to tell your housing office. Sort out maintenance from your ex partner ASAP don't be afraid to ask. If he declines call the CSA.
I was in your position in August so I can tell you what I did if its any help.
Ring tax credits asap and cancel your joint claim and make a new one from the date of the split. That will automatically sort out NHS low income exception cards and you should get a letter from healthy start that you need to get signed by a heath visitor and send back and that will get the fruit/veg and vitamin vouchers for the little one sorted.
Ring Income support helpline and start a claim as soon as you can. They will register you, which gives you a start of claim date and send you a form which you need to fill in as quickly as you can and send back to them.
Ring the council and ask for a council tax benefit form, if you rent this is the same form as you will use to claim housing benefit. they told me they will pay council tax benefit from the Monday after the start of an income support claim and they'll back date if necessary but I'm guessing you need the money so get the form in as soon as you can.
If you have a mortgage you need to fill those details in on the income support form and they will send you another form about mortgage interest help.
My tax credits took less than a week and was done all over the phone, the income support took about a fortnight and the council tax benefits took about three weeks once I sent the form.
Good luck sorting all the paperwork but try and keep a list of date you apply so you can tick them off once they're sorted out.
Not sure if that's any help but good luck with it all
Have very recently split with my partner and now a single parent to 22 month old ds. Split is amicable and hes being great, but im soooo confused!! Ive been a stay at home mum since ds was born and have now been faced with a whole load of ridicuously confusing benefits etc that i have no idea about. Just wondering if anyone knows anything about entitlement and whats the best way to go? Anything that i should be asking for etc as im totally new to this. I know ill have to claim income support for a while but thats as far as ive got really :/ Any advice would be so greatly appreciated. Would just be nice to speak to people who have actually been in this situation rather than an advisor over the phone!