Wheels are different yes - 225/40 r18 on front and 255/35 r18 on the rear - same as Premier and F-Sport models.
The IS F-Sport rides better than a CT advance and therefore you can imagine that the Sport rides better than all CT variants
There is no suspension change between Sport, Luxury and Premier. Only the F-Sport gets stiffer suspension.
If you are set on the IS300h Sport, may I recommend Broadspeed? They've got £4419 off list price so you can get one for £25775 + paint
Having said that - I should mention that there is a new model coming out later this year/early next year called the UX250 and UX250h. Its a small SUV based on the CT