Grobags can provide a convenient alternative to layers and are less restrictive than swaddles can be. They also prevent the baby from kicking off blankets and needing to be re-tucked in if the weather is cooler.
They are essentially a baby "sleeping bag" with arm holes which prevent the baby from slipping down inside the bag.
They can be used to newborns (though aren't often recommended unless there's no chance of the baby slipping down into the bag) but are growing in popularity for older babies.
The Devon-based grobag® company work to ensure safety and follow guidelines on nursery temperatures. They also work in collaboration with FSID to a provide safe sleeping option for babies and they're the only baby sleeping bag that FSID endorse (though they don't recommend them any higher than layering - it's for parents to decide).
They come in various Togs which indicate how warm they'll be. For this reason you'll need different versions depending on the season and the age of your child.
"Mums love them." says midwife Sue MacDonald but warns that it's still important to ensure babies are not getting overheated and to check that you have the right Tog.
Prices start at £18.39 direct from grobag.