Recently had a FIRA tech report, can you advise about bases?

Recently purchased a 4'6"Sealy Guernsey mattress and been used now for 8 months one sleeper only. Side, back, front sleeper as osteoarthritis in knees, hips and discomfort in shoulders. 2.3cm settlement already. FIRA technician said I need support legs below central rail (slat gap 7/7.5 cm base ok). I was never told /asked what base I was using when I purchased this mattress. Can you give me your opinion as I need guidance on the matter.
Thank you.