Luxury Firm - not firm enough!

Based on a suggestion from my chiropractor, we purchased this mattress about five months ago. Because I have a 'bad back', we went beyond the 30-day return cutoff, blaming my back and not the bed. This bed has never felt comfortable and my assessment is that it is too soft. The quality is fine and the customer service is great. When I finally called the company, they offered to send a firmer mattress to the tune of $240. We get to keep the luxury firm mattress. The firmer mattress has arrived and it is better but not great. Since we have already invested so much money in this mattress, I am looking at adding a foam topper. If I lay on my back and don't move all night, my lower back is ok. I cannot sleep in any other position on this mattress without tempting the 'Back Fates'. I would dearly love to find a mattress that made me love getting into bed. This is not it. A word to the wise.....keep an eye on the calendar when trying out this mattress. If it doesn't feel good within a week, it's not going to get any better. I should have followed my own advice. I will be trying out foam mattresses for the next several weeks!!