The coupe has a bit more room in the back than the convertible, although I can imagine doing my back trying to dig a car seat out of there!
The main problem with the 997 interior is that Porsche seriously upped their game with the 991 interior! I find the 997 interior very comfortable and pretty simple. The only thing that could do with freshening up is the AC panel and PCM, but the more I use PCM 2.1 the more I can see myself keeping it and spending the cash on a nice induction kit instead. It's been quite nice putting my CD collection to good use!
The 991 is lovely inside but I think the PCM3.0 of the 997.2 totally transforms the 997, fortunately for me its just a booster that sits there all the time, i'm not exactly a lightweight but could just about get in the back (alone) for a short trip into town if the wife was dropping me off, I remember clearly about 15 years ago sat in the back of a 996 from Newcastle to the NEC and back in a day, took a while to recover...