After I posted up last night I lay in bed for ages trying to think of something constructive to offer (sorry if I was negative!) It sounds like you're spending the absolute minimum already, so I guess what you really need is to find some way of getting some more money in, which can go towards your savings.
I used to have a friend in the UK with two small boys who used to do the following - don't know if it would work for you, but I know she made quite good money at it:
She used to get up early at weekends and hit three, sometimes four car boot sales. She was looking for baby equipment, mainly mamas and papas pushchairs as she knew they were well made. She would buy these at car boot sales, primarily looking for ones in good technical shape, that maybe weren't all that clean, take them home, clean them up really well, get her husband who was quite good with mechanical things to give them a "service", and then advertise them for re-sale, mainly on the free supermarket noticeboards, at a good mark up from what she'd paid.
This worked for her because (a) having small children of her own meant she knew all about baby/child equipment from personal use, (b) she could take the kids with her to the sales, or leave them and her husband in bed, and (c) the "value-add" was her time and effort - most people selling at boot sales tended to sell stuff "as was", so with a bit of time and elbow grease, she could make the product look much nicer, and therefore worth a lot more.
Don't know if this or something similar would work for you - of course, that was in the days before ebay really took off, so that would now be another sales outlet, but if there is something you know a bit about, it might be possible to adapt the idea. If boot sales are still as popular in the UK, and if there are some in your area, might be worth looking at.
Another thing I thought of was that sometimes the WI run weekly produce markets, so if you can cook (and to feed your family for that little each week you must be a whiz in the kitchen), you could bake cakes and sell them there, or if you grow your own veg, sell the excess.
Dunno if any of that helps, but felt really bad about being negative!