Brand new too soft Harrison Bed

Hello, I'm looking for a bit of advice please. My husband and I have just bought a brand new 12700 Spring Pocket Harrison bed. He has the medium firmness and I chose the gentle. Having tried the mattress out in the shop the gentle felt right. However having slept on it for 2 nights now I feel it may be slightly too soft while my husbands side is slightly too hard. I think the problem is that I'm inbetween the two choices and require a soft/medium firmness. The bigger problem is that our mattress is non-refundable and was extremely expensive so getting a new mattress at the moment is not an option. I'm hoping you'd be able to advise me on how to make my soft matress slightly firmer. We have the mattress on a divan base. I weight about 10 stone after having my last baby (but I am currently working with a trainer to lose a stone). My weight is normally 9 stone to 9.5 stone. Will losing weight help with my problem? What can I do in the meantime to help? Thank you in advance for your time. I found your website very helpful and will recommend it to my friends.