Guidance on new bed.

Hello. I am hoping you can give me some guidance on a new bed. My husband and I currently have a king size Hypnos Sleep Safe divan with "regular" support. I am ashamed to admit it is now 16 years old so you might not even have heard of it! Both my husband and I suffer periodically with back pain but as our bed has got older I wake most mornings feeling incredibly stiff. We recently stayed in a holiday cottage where the bed was beautifully soft - the type you sink into - and I had the best weeks sleep for a long time and no stiffness in the mornings. Although my husband was not as keen on the overwhelming softness as me, he did comment that he found it more comfortable than our existing bed and perhaps a half way version would be good for him. Following on from that we decided that perhaps a zip linked bed would be a good idea (king size) which could have a softer side for me and something suitable for my husband. It was then that I discovered your website. We would be very grateful if you could point us in the right direction. In terms of weight, my husband is 13 stone and I am 9 stone. We will be requiring a new base and possibly headboard as well. Many thanks.