Royal Canin do several million cat foods (and we've tried pretty much all of them), the ones that would be relevant to your friend might be;
Light 40 (bog standard light food), Sterilised 37 (light food for neutered indoor cats), Intense Hairball, Indoor 27 (light-ish food for indoor cats) and Indoor Long Hair 35. Pure Feline no 4 Wellness is good for hairballs too.
The Horde are currently on a mix of Sterilised 37, Digestive Comfort 38 (stops Mao vomiting it back up) and Pure Feline 4 as Homer does really badly on foods other than RC. We've tried everything available on the market over the last 4 years and I even gave raw feeding a go but it's RC or nothing for Homer.
I've heard good things about Orijen too but they don't do a specific light food.