It looks like you're trying to budget for everything not just baby costs, the best way to do that is to keep track of your current monthly spend, then you will have an idea on the cost of your essentials and be able to add baby costs to it.
My dh is an accountant so in our house every penny is recorded but it means at the start of a month I know how much I have for pleasure spend after bills etc. I spend £300 per month on food for the 2 of us (Tesco) so your £200 sounds reasonable to me but everyone is different. I have also started to think "what additional costs there will be with baby", ie fuel bills will go up as the heating well be on more, plus stuff I will buy for baby, but I hope to get stuff second hand. I think you make a baby fit the budget you have, sounds like you're being sensible to me.