I would contact an organization that arranges for families to "adopt" a family for Christmas and apply to have your son "adopted".
You're not a shit Mum, you care enough to be concerned. How about wrapping a few toys he has now and give to him, that way you can take pictures and get him all excited about it.. Turning 1, he's going to be more interested in the paper anyways :P and if he ever does ask for pictures when he is old (which I doubt he will) you can show him :) Christmas is all about family and he has you both which is more important. Make a whole day of fun thats just for him... play-doh, painting christmas shape cut outs, going to the park, watching a movie, snuggley story times etc.
There is always next year!
I know how you feel. We have had to cancel xmas 2/4 xmas my Ds had because we couldnt afford it. Last year somebody nominated us fo adopt a family so you might want to look into. Btw Dd will 8 months in december and im only spendin 100dollars on her just enough so her brother doesnt wonder why she doesnt have as many presents. they wont know the difference.