OP did not have pics of the worn seats or what the timeframe for ownership would be, so my comments are for the long-term timeframe.
If you go to a salvage yard, most of the good seats gets snatched up quick, so what's usually available by the time you get there is just as or more worn out than what you've got already.
OEM cloth and leather seat covers were available a couple years back through Camelback or Conicelli Toyota online parts order. But at least for the oak color, it looks like they are discontinued.
However, the cushion foam is still available for both the seat and the seat back at Camelback, Conicelli and Sheehy Toyota of Fredericksburg.
Seat Cushion Pad - Toyota (71511-35050)
Seat Back Pad - Toyota (71551-35050)
If your passenger or back seats are still good, switch between sitting between the driver seat and those other seats and decide for yourself the age of your seat foam.
If your time horizon for ownership is "till the wheels fall off," something to consider is buying the OEM cushion foam, then buying an aftermarket seat cover in the fabric/color of your choice. You can use the search function to look up seat cover recommendations in this sub-forum. Also, there are numerous vendors on eBay.
If you have an auto upholstery shop near to you, find out how much they would charge for just the labor if you provide the foam and covers.
There are a couple of YouTube videos that show you how to DIY, but when I had an auto upholstery shop do it, it took them 2 hours. So, I decided paying was worth the time savings of me trying to DIY.
All total, I paid around $750 for new OEM foam (seat & back), new leather covers (from eBay; seat and back), and the labor to replace them. For me, it was worth it to get a brand new driver seat!