How much electric you will use is dependent on so may other things!!! What you wear around the house is a factor and how much you feel the cold? DH would wear next to nothing and feel hot, whereas I could have a jumper, vest, trackies and wooley socks and feel comfortable.
Is it double glazed, how large and how many windows, where in the country, what storey is the flat, carpets, underfloor heating etc etc. Whether it is rented or bought, you should have been given an EPC rating to see the rough energy usage! Did you get this?
We had a large, 2 bed flat in central london. It only had external windows on either end of the property, so very enclosed in most rooms. We did notice if our downstairs neighbour was out, because our flat was so much colder, so you might find it does get warmer when others start moving in.
You will likely be better to leave the thermostat lower, but leave the heaters on longer as another poster suggested. Another option is to buy oil heaters which aren't as good as storage heaters, but do seem to keep warmer for longer than electric styles.
For a 1 bed, I'd start with a lower electric amount, and add on if needed. It seems more difficult to reduce your direct debit, than to raise it in my experience.