Old Coachouse, single glazed (!) Oil heating - would i be mad ?

[escape]

Desperately unhappy in our little rented place, it's just not big enough, I hate clutter and with 5 of us in it, it's inevitable.
I have been battling for ages about 'taking the plunge' for a bigger place - the problem is price..
At what I am paying now - the next 'step up' price wise is an approx £300 cpm rise,
I am the kind of person who will spend forever thinking I 'Can't do it' - but I am so unhappy, I am making plans as to how I CAN do it.
I work from home, I know no-one in my area , the schools are 5 mins each either way, apart from this I barely leave the house Mon-Fri - I NEED to be happy in my home.
SO - I have seen a lovely place - £300 cpm more than I pay know, council tax the same, but I really can't afford to pay any more on utilities etc than what I do now.
As is the area, it is Oil heated from a tank - the glazing is single ( the windows are not even UPVC
Would the oil bill be extortionate?

you will loser more heat from the walls, which are almost certainly single-brick with no cavity.

Walls are much bigger than windows, so are the first thing to look at. Worse still if it is a detached building.

You could fit low-cost plastic film d/g over the existing windows if you wanted to.

Oil will be more expensive to run than GCH.

We live in a 400 year old house, single brick walls, only secondary double glazing on some windows, most windows are ancient leaded lights.

We pay £90 per month for oil, and have a wood/coal burner.

Thanks ladies - never thought about the walls - there are large radiators in most rooms and a brick fireplace in the lounge...