Marmalade you can eat exactly what you like. But do check that places are open.
In your shoes I'd still prefer to know what I was having and either have it ordered or something simple to cook.
Like duck breast in orange sauce or nut roast that you simply wack in the oven for a set time with a jacket potato.
If your mum is coming over what will she eat?
At the very least please do buy yourself some nice chocs and a nice pudding/dessert if you like sweet things! 
Please do not take this the wrong way, but you sound a little depressed, could it be post natal depression? If you are at all concerned that this could be the case, please do visit your GP after Christmas.
The bottom line is do what makes you happy tomorrow, tree , no tree, whatever, but look to getting things better for you in the new year, counselling or whatever may help.
Babies can be quite tough, lone parenting can be very tough too. You are not wrong to feel under pressure and YANBU to want to make tomorrow easier.
Please do find some bright spots if you can. The penguins of Madagascar is on TV today, very good - It's a wonderful life is on TV tomorrow. Find some top TV, nice chocs, lay off the wine and take some beautiful pictures of your baby and your mum. Babies grow so fast . Find some points of light. 