Upgraded
struts & springs can really improve overall comfort.
Quality tires with a respectable sidewall profile will also contribute to a comfortable feel.
In regards to interior comfort, I cant speak for the comfort of your generation seats, but its a bit excessive to swap seats solely for one long drive if they suffice for daily usage. Hence, I suggest a simple
lumbar support. I personally love the lumbar support posted below. It sells for $10-$15 in pharmacies and Bed, Bath & Beyond stores. It breathes well and is very comfortable. I drove 17 hours straight due in large part to using that same lumbar support.
If you insist on
swapping seats, I can attest that 2000-2006 Honda Insight seats are very comfortable. They're pictures in my signature. You can click on the hyperlink to better view them.
Window Tints will also assist in keeping the cabin at a more comfortable temperature.The windshield also allows alow of heat penetration so you may consider using a 70%+ UV tint solely to block out heat. Do note that tinted shields are illegal in most states but if its light enough it may go unobservable.