No worries, have been through a couple of cheaper Vango bags and whilst they do the job they are heavy and not as well made,
The Decathlon bags look good as well, If I was on a budget I would buy one of those and spend more on a good sleeping mat – you will lose more heat to the ground than to the air, so a good sleeping mat will boost the warmth of your bag.
Depends on weather or not you will be doing a lot of camping around all year or just in summer.
Buy the kit that fits your needs, generally buy cheap, buy twice rule applies with ‘most’ camping equipment.