I'll try to put my two cents in.. I hope it helps!
I ride horses so I am really knowledgeable when it comes to leather care. I mean, hello, saddle, bridle, boots, ect and I believe those are harder to keep in "great care" than what you sit your butt on everyday and we can't have our saddles/boots/ect. be sticky.
If you are willing to order something online, hop on over to Leather Care - Dover Saddlery
I usually use cleaner, conditioner [to lightly condition] and then to really keep my riding leather supple, healthy, and comfortable [and it doesn't get gross, promise], we use leather oil. Conditioner will generally make your leather "stickier" while oil will make it more smooth [makes sense huh?] You just have to really ensure you use a VERY small amount of oil. I use about a tablespoon for my entire saddle. We usually oil saddles when we first get them to supple the leather.
Make sure you don't get anything that says "wax" on it. Us equestrians use this "wax" to give us grip on our saddle so our legs don't slide around.
If you are just looking to pick some up locally, at like a grocery store, Lexol CLEANER will do the trick. The conditioner may make it tiny 'sticky', not too sure. I usually use local brands that I know work beautifully so if you really were desperate I could have some shipped to you because they work absolute wonders.
Instructions on how to use each:
-Cleaner: Wet your sponge and the wring it out and wipe down your seat/leather. Rewet sponge and wring out to where it is damp. Spray/apply cleaner onto SPONGE. This will be easier on your leather than just spraying straight onto the leather itself. Knead the sponge so the water and cleaner mix [don't get it too foamy] and then just gently wipe down your leather. The purpose of many leather cleaners are to remove grim, and unless you are using your IS as a mud vehicle, you don't want to overdo it so it doesn't dry out. Once you're done wiping it down, do not let it sit! Wash out your sponge and wipe clean. Then towel dry with a microfiber cloth/lent free cloth.
You will either next apply conditioner OR oil. Not both.
Conditioner: Pour a very small amount onto sponge and work into dry leather. Let sit for about ten minutes then buff with a towel.
Oil: Pour a small bit of oil onto your fingertips. Your fingers will apply it better than any sponge/cloth out there so you can work it into cracks as well as your fingers won't hold the oil like a sponge will, so there isn't really anyway to overdo the oil. Work oil into dry leather really ensuring you massage it in to were the leather "drinks" it up, otherwise you will just have pools of oil sitting on your car seat. Let sit for about ten minutes and then buff with a towel.
Tomorrow I will update and speak to some representatives on what soaps/conditioners will be the best, considering it's 1am right now. :D
Hydrophane is the best oil you can get.
I hope this helps some. My riding tack goes through hell and back and it still looks great, but that may mean that the cleansers I use may be overkill.