I recently purchased a used 2013 MKX and found the same issue in the driver seat - very hard and uncomfortable especially when coming from a 2019 Ford Edge with incredibly comfortable seats. What I find strange is the right side feels as thought there is a support bar / seat frame or something that goes across my butt, but not all the way across, whereas, the left side doesn't have that. Has anyone else experienced this and if so have you been able to add any cushioning in that area to make it feel better? Maybe it's just me as @akirby would say, but I thought I would give my 2 cents.