We’re hopefully getting a couple of kittens from a sanctuary soon and they recommend chicken feed! Much cheaper, easy to bulk buy, flushable etc. We went to see the kittens yesterday and there was no smell at all from the litter trays
I bought a large mat which was the only thing which truly made this problem go away. Anything that didn't track, one of my cats refused to use. My bigger cat is a nightmare since he spends ages rearranging the litter after going sometimes (he came to wake me up with litter on his face the other day due to excessively vigorous kicking).
I use Cats Best Oko. It's a bit redundant at the moment as my cat now has a cat flap and has his favourite spot in the garden (I'm still 'scooping' but it's now from a flower bed- not much fun!) I found it was great. It clumped brilliantly and didn't smell as long as I scooped the clumps once a day, and decently filled tray would last a couple of weeks before a full clean and change ( it says it can last up to 4 weeks before a full change but I felt bad leaving it that long). It seemed to 'track' to just outside the litter tray and I'm pretty sure that was due to my cat kicking it out whilst trying to bury whatever he had done.