If you're on the sick, then you cannot be forced to attend the meeting, as it's officially work and you're officially not supposed to be there, no matter how well or otherwise your store is doing. When your current sick note ends, if you still really cannot face work, then go back to your doctor and ask for another one. Do not let your boss bully you. If he/she writes to you, visits you or phones you at home, keep a record of this and try not to get into a discussion about the matter.
Get your boss, or, in the event of his/her likely reluctance to do so, the company's HR department, to refer you to an occupational health specialist, which you have a right to see. Failing which, you can refer yourself to them - again, you have a right to do this and it ultimately puts you in a stronger position. They will arrange counselling for you, if you feel the need to use it, and will act as an intermediary between you and your employer. My bloke's been going through something similar of late and OH have been a real lifeline for him.
You should also be able to get some help from your trade union, if you're in one. This is what they're their for.
As for your landlord, I'm not sure where you stand re. housing benefit. I know my rental agency tends not to accept new tenants who are on housing benefit. Maybe your local council's housing department would be able to advise you here. I'm not saying you'd immediately get a council place, but they could at least point you in the right direction. Social services may also be able to advise, maybe a combination of both departments, depending on the departmental structure of the council.
Take comfort from the fact that eviction isn't a speedy process. The whole process, from start to finish, typically takes several weeks, maybe around three months, and if you're trying hard to keep on top of your rent then a court is likely to come down in your favour.