Which Artisan mattress suitable

Hello. I'm interested in your Artisan mattresses, but am unsure which mattress tension would be suitable for me. I am 9 and a half stone and my current bed is too firm for me. I am worried that if I get a Soft tension mattress it might be too soft for me, coming from a less giving mattress. However, if I used the platform base from my current bed, might this make the Soft mattress a little 'firmer' or would it spoil the mattress because I wouldn't be using a sprung base? I'd be grateful for your advice. Many thanks.