A medium/hard mattress, such as this one, is generally good if you weigh 80 kg or more. This particular mattress measures 90x190, so make sure it fits your bed.
From Mattress Online
Silentnight Just Breathe Eco Comfort Hybrid Mattress, Single
John Lewis & Partners
Silentnight Just Breathe Pocket Spring Mattress, Medium/Firm Tension, Single