Well done OP. It feels much better when you know your position and are able to take steps to get it under control, even if the situation seems pretty tricky. Stepchange and CAP (Christians Against Poverty) are great places to start for advice on your debts. You don't need to be a Christian to go to CAP, it's just where they started from.
Look at where you shop. We use mysupermarket.co.uk to compare prices and have recently switched to going to Aldi and Lidl. I can get a load of stuff for £50 and lots of it is excellent quality. Definitely worth a look. There's also an app, so I have my shopping list on my phone as I go around so any swaps I need to make, I know what I was going to pay for the item and can choose an appropriately priced alternative and not go over budget.
Good luck on the car swap too, definitely worth doing. Sometimes adding a parent on (depending on age & medical issues etc) can help bring down insurance too. Also look at what DH's job is listed as, obviously don't lie, but some jobs attract a higher premium and some jobs fall under a couple of categories, that can give you a bit of wiggle room on the quote.
Giff Gaff are good for sim only deals and also phone contracts too. They're month by month and you can go up/down tariffs every month if you want. Ideal if you need extra/less at different times (I've got a £20 20GB data one this month as we're on holiday relying on 4G, next month I'll go back to my £7.50 tariff).
Also check out cash back sites when swapping utilities, you can get some money back if the quote is also a competitive one you were going to get anyway. Takes some time for the money to come through, but can be worth doing.