My advice: don’t buy a mattress sold on TV. Go shopping wearing comfortable clothes suitable for testing mattress comfort and pick the one that feels good and you can imagine sleeping on for maybe 10 years.
No matter what the features are as described by QVC, comfort cannot be proven viewed through a screen. If the price for the Serta TSV is just right, use it for a guideline to purchase in person so you won’t be upsold by a mattress salesperson.
Valley in the middle after short use is a sign of a cheap, poorly constructed mattress. You can buy one in person or on TV if you don’t ask questions and do some prior research to know what materials and manufacturing methods are ideal. Determine the warranty conditions as well.
Good luck and good dreams!