you may have done the flowers and breakfast in bed but that doesn't mean if you've done it once thats it.... i am 100% sure your wife would still love both of those things.
As for your son why dont you help him make something for his mum, even if it's just the card, anyone can buy a card in the shop but the items i treasure most are the things my children have made for me over the years.
Does your wife have a favorite restaurant she likes? Or weather permitting you could go for a picnic ( dont laugh the weathers not that bad at the moment )
I suppose it depends on what your wife's likes and dislikes are. She could want to go out for the day. She might just want to stay at home. I personally like staying at home with the family and being waited on hand on foot ( although that never really happens )