Comparison to the NEXT 1000 pocket sprung mattress

Hello!
What is your opinion on the NEXT 1000 pocket sprung medium tension mattress?

–1000 individual pocketed springs which independently respond to provide support where needed
–Turnable –Keep your mattress in tip top condition by flipping and rotating on a regular basis
–Layers of soft white polyester and natural blend fillings
–Covered in a high quantity cotton rich fabric
–Traditional tufted finish

I stupidly purchased from Benson's a few months ago, it turned out to be faulty and they're refusing to refund me, so I'm having to cut my losses and start again. £1500 down the drain! I wish I knew about you before!
I now only have a budget of £600, which is why I was looking at the Next mattress, as it's only £475 for a King Size, and is turntable (as you suggest is always best).

The one I had from Benson's was a firm tension and after just one night (I persevered for 45 days!) I was in complete agony: shooting pains in my shoulder, hip and thighs. It was obviously far too firm.

I'm a side sleeper, it's just me in the bed, and I'm 5ft 6 and weigh 8st 10lbs.

I've tried a memory foam mattress and I get far too hot.

Please help as I've had 5 months of mattress stress, caused by the crooks at Benson's. They eventually sent out a Fira agent and have agreed the mattress is faulty, but refuse to refund me, they will only swap it for a like-for-like... which is far too firm (the salesman pushed me to get a firm!!). All I can do now is accept the exchange, then sell it on eBay, probably for less than £500 (I paid £1499), hence why my budget is now dramatically reduced.

I'm so upset and stressed with it all. All I wanted was a nice comfy mattress, as I have insomnia, and was hoping it would help me... it's done the complete opposite! :-(