Which bed tension?

Hi. Thanks for such an informative website. I am 9.5 stone side sleeper and I’m unsure which mattress to go for. My current bed, which is about 14 years old, needs replacing. I can’t find much information about it other than it has 1000 pocket springs. It has served me very well but now feels uncomfortable when I sleep on my side. I am confused about which tension I should go for if I get one of your Artisan beds. Should I go for soft or medium? Would soft be better if I use a platform base? Or would medium be better on a spring base? Or maybe soft on a spring base?! Would the Origins 1500 be suitable also, do you think? Or even the Origins Comfort? Sorry for all the questions! Thanks in advance for any advice.