I recently bought 2019 Limited. I was really in a dilemma whether to wait for 2020 or go for 2019. But the deal that I got on 2019 played a big deciding factor as I was on a tight budget. I don't think I will repent, because I can't see any deals on new 2020 coming in the nearest future. So I am happy.
Now to answer the OP's question, yes the seats are comfortable. Before purchasing my vehicle, I drove 2019 Highlander XLE for a 2K mile trip, it's when I fell in love with HL. The total trip was so comfortable, we never felt fatigued or tired.
I drove lot of other SUV's extensively (mainly because of the nature of my job), so based on that experience I rate HL top in the line. you may find, QX60 seats more comfortable but it comes with a lackluster engine. The only other SUV (in this particular segment) that I would prefer over HL is CX-9, but I don't like turbos which was a deal-breaker. when I wanted a 3-row SUV, I decided to go with Toyota HL if it was for a purchase, or go with CX-9 if it was for a lease. So my decision was easy.