Feel every inner spring!

I purchased the Simmons Black Beyond Earlington Firm mattress because I thought it would help with back issues. I had knee and hip surgery in the last two years, and I find that both areas are very painful now. The mattress feels as though the springs are poking into my ribs and hip and I awake feeling exhausted. I'm really disappointed as it appeared to be such a great mattress; the quality appears to be very good but it is the most uncomfortable mattress I have ever slept on. I will likely change it for a Marshall as I have only had it for 2 weeks and the reviews for the plush pillow top in Simmons are not great. Also the salesman advised me that the pillow top has considerable "sinkage" in the middle after a few months. Don't want that so will go with a mattress I can flip. Non-flip idea was a sales feature for me until the sales associate said that it was great for the company as the mattress would need replacing sooner than one which could be flipped- good point. Hate this mattress and can hardly wait to get rid of it.