Coincidentally, I live alone in a maisonette with my dog and work full time but over the last 4 years I rarely had the meter reading taken and I got estimated bills all the time. I recently went back over the last two years invoices and calculated around Eur80 per month average so I am putting Eur100 away each month to cover it and obviously the little extra just in case my calculations are wrong (based on the estimated readings). I am the named occupant and I pay by direct debit so they give a small discount for that. I missed the meter reader the last time (again!) but this time around, I actually submitted the readings online and my most recent bill for three months was Eur35! Obviously that estimated readings were way off but until I have the meter read and have a look at future invoices, Im not really sure how much I 'use' per month so difficult to say.
After typing all of the above I just realised I am rambling on here and not really having a point or an answer to the original post! sorry