Back problems and continued poor sleep advice on bruno mattress

Hi.I am 5' 7" inches tall and 11 stone.I have a chronic and severe back problem which I manage with exercise etc but I have ignored the importance of a new bad and mattress foolishly.
I recently purchased a "bruno" mattress and placed on my old wooden slat base and though it is quite comfortable for a short period of time, I have found it both too warm even with new cool bed sheets and pillows and is also unsupportive in my lower back causing me some spasming at times.Due to this, I tend to sleep in a side on or foetal position but this contacts my muscles when extension of these and sleeping on my back is a preferred option if possible.I am not wealthy, but for the right option, I would be willing to look at what ever option is best as my back affects adversely all daily tasks and I sleep poorly.
I am an Occupational therapist in neurology and aware of the importance of anatomy, alignment etc but have not practiced what I preach to my clients.Based on your fantastic web site, I have been looking at the origins latex 1500 mattress and also considering a new base and headboard to complement it.Do you feel this a correct choice or is there values in purchasing a artisan. I do get hot in bed?
Would I be better off getting a more expensive mattress and just place on my old timber slat base or is this a poor idea?Additionally, I am having a major knee operation on the 13 June and would the base and headboard be put together and delivered upstairs by yourselves as I could not manage this?Also if I ordered this week, could you delver and fit before my operation on the 13 June?
I am quite desperate to find a solution or something to improve things as I am getting no more than 90 minutes sleep at a time so I would really appreciate an urgent responseI think this resource is fantastic and much appreciated.All the bestRob