my step aunt works for DWP and has tons of experience with benefits - quite high up, writes lots of training materials. she is on hols abroad till this weekend, but I will try and speak to her this weekend about it if you like.
my first thought would be if you could get signed off with depression and claim any sort of incapacity benefit. but I know very very little about benefits so that might be completely the wrong thing to do...
i would try and stall your work until you have had a chance to speak to somebody like CAB, just in case, as pixiefish says, they way that your employment ends has any significant in benefit terms.
i think you are doing absolutely the right thing as well. if you do go back to work, you need somewhere that's more supportive to you and your family's needs - atm you seem to have all the disadvantages of a small co in terms of pressure on you to return, and none of the advantages of leeway/sick pay etc.