On 01/10/2017 09:32, Graeme wrote:

Time for a new king size mattress, ours being rather soft and many, many
years old.

Firm support is the way to go, but any recommendations, or types to
avoid?Â* Looking at John Lewis, where they start around £250 and go up to
silly money.Â* Are those in the £300 range acceptable?

Only you can decide.
Try them.