When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have lumbar support all the way up and its very comfortable on short stints but as the OP says I feel some discomfort in my lower back on long drives.
My F-Sport seats are probably the best seats I've ever had in a car. Every other car would give me lower back pain after an hour of driving, but not in my IS.
Keep adjusting the seats and trying out the positions until you find something that is better. I was having the same issue as you (and I drive about an hour each way for my commute, so I spend quite a bit of time in the car) and my lower back and neck were hurting every day. I learned that if I raised the rear of the seat slightly and adjusted my lumbar it made a world of difference.
Now I absolutely hate when anyone moves the seat because it takes me a day or so to fix it. Yay for no memory seats :-(
I have a 2014 F Sport and drove from Vegas to LA on Tuesday. I felt the car was very comfortable and quiet. I succumbed to the need to urinate and stopped in Phelan on the way back. I love the car. If it was a 350, I would buy it. It's a 250, so Lexus is getting a really nice car back in July and I am getting a 350.
Who else think the seats on the 2014 IS250/350 are uncomfortable on your lower back after about an hour of driving?
Also, don't know your age, but that is irrelevant. Look at Egoscue.com to fix your back. There is a book called Pain Free that will get you started.
I am a 45 year old guy who played club level soccer in CA and had some back issues. I am comfortable now and don't stand to make a dime by steering you to Egoscue. I am only mentioning it because it may help.