I don't think its a case of being reasonable or unreasonable. Either you can afford to stay at home or you can't. I think you need to check out Girlysquare's link and see whether it adds up.
If your DH's pay is 35K, presumably after the mortgage that would leave 950/month to live on. You need to work out whether that money would cover bills and other unavoidable commitments, food, clothes, house repairs, transport, running a car.
How much will be left over for holidays, Christmas and birthdays, toys?
Are you prepared to cut out little extras like magazines and coffees?
You also need to calculate how much money you earn after nursery fees, your travel costs and any other work related costs. This is the amount of money that you add to the pot. Would you be able to work part-time? Do you do the kind of work where a career break would be practical?
At the moment I can afford to stay at home. However, when DS was 5 months old I had to return to work. Yes, it would have been great in some ways to have been able to be at home then, but on the other hand, sometimes its necessary to put food on the table and a roof over your child's head, and thats great too.