Does physique/body proportions matter when choosing a mattress

Hi,
I just bought the medium artisan naturals with a pocket sprung base, going for as much comfort and quality as I can afford and praying it will help me when it arrives. For the past 6 years now up to this day, I've woken up literally every day of my life feeling physically and mentally exhausted, fatigued and lethargic. I realised my beds weren't perfect all along but I also thought it was other health issues that were causing my sleep problems, completely overlooking how important the bed actually is.
Only by recently discovering the wealth of info on here during my desperate, sleepless nights have I realised that all my health problems are symptoms of poor sleep and poor bed choices and not the other way around. No matter how much healthy eating, yoga and meditation I do, I struggle to either fall asleep or stay asleep, and even if I do get 8-9 hours of sleep I still feel like I've only slept for about 4 hours.
The first bed I had was a cheap, poorly constructed wooden-slatted frame with an equally cheap, possibly medium mattress which was obviously nothing special. I eventually bought a £120 medium-firm memory foam mattress from memoryfoamwarehouse and placed it on this uneven, wonky bed frame which of course turned out just as uncomfortable. I often woke up too warm which I wrongly assumed was the sole reason for not sleeping.
I eventually got rid of the bed frame realising it was the problem and put the memory foam mattress directly on the solid floor after learning they're better with solid support and while waiting for a new bed. Now in the few days that I was on the floor on the foam, there was just one morning where I woke up feeling absolutely amazing and alive, better than I've ever felt in my life, but I've never experienced that again.
My new bed arrived shortly after which was a firm 800 pocket sprung mattress and terrible divan for about £300-400 from carpetright and of course this turned out to be no better. I took some bad advice from family, various internet sites and a useless store assistant which all had me make a completely uninformed purchase and ditch the memory foam mattress. Even with a luxury silentnight memory foam topper, this firm mattress was still bad and I have since got rid of it, and for months now I have been alternating between simply the foam topper directly on the divan and an airbed.
I then thought maybe my shoulders are just too broad to sleep properly on my side since my shoulder tends to get squashed and sometimes my ribs hurt and I've read of other people struggling with that problem. However this can't be true if I slept so well on the medium-firm foam mattress, and perhaps those other people simply haven't picked the correct bed either or they are huge bodybuilders. I am about 5'9", 12 stone, and my shoulders measure 49 inches compared to my 33 inch waist, I really don't know if that is considered broad. I prefer sleeping on my side and sometimes front, although I find myself rolling onto my back likely due to the bed being too firm and worse than a prison floor.
So really my questions are:
1. Considering I once slept so well on a £120 medium-firm memory foam mattress, and considering I've never really slept on a proper medium or such a high quality bed as the Artisan Naturals, do you think your luxury medium bed will truly solve my problems? And will body shape/physique even matter?
And also:
2. I've read the best way possible is to sleep on your back with your legs elevated at a 90 degree angle. I've tried it and it's just too impractical without something like one of those chiropractor tables that raise your legs. What is your opinion on this compared to sleeping normally on a luxury bed?
Thank you so much for your help and all the info on here, I'm really looking forward to this bed arriving, hopefully a few more sleepless nights will be worth the wait!