OK I didn't appreciate that you were both working and the two figures at the top were two incomes.
Still, though, on that income you should be getting some tax credits, if you had similar income between April 2016 and April 2017 to what you have now.
Are you based in or around London? Regardless, can you move to a smaller property?
One bed is not brilliant but it is sufficient for a couple with a small child, unless there are additional needs and/ or other children are coming to stay regularly (you mentioned maintenance).
Even where I live (a relatively expensive London suburb) you can get a one bed for about £300 less than you are paying per month. I appreciate that you may not have the option of breaking the lease but as a PP said, if you are more than 6 months in, then that might well be an option.
The main option would seem to be trying to earn more. £11,000 p/a is not much, it's pretty much minimum wage isn't it, if you're working 40h per week. What job do you do? I think this is your best bet, bringing more in rather than trying to make not very much go further.
Your DH or you could earn more than £11,000 p/a as a nanny with own child or a childminder who took up to their maximum allowed ratios, to pluck a couple of random examples. I know it's not that straightforward to change career direction but really, you are not going to have an easy time till you're bringing in more.
Is he being tax efficient if he is self-employed? Is he making sure to deduct anything he is allowed, etc?
Ebay/ Schpock/ Gumtree everythhing that isn't nailed down, is my other tip, and never buy new clothes/ shoes, as they suck up huge amounts of money.