Pretty much. The only time I've seen a cat messy is when they have an accident or bring a couple pellets out from the litter box. They sleep and clean themselves all day. They are really clean (you should still give them baths and brush them of course). For the really long haired cats we would always have the hair around their butts cut really short so nothing would get tangled up.
Both of mine kinda crash with me depending on the situation.
BTW these are Long Hair Chihuahua so they are like 5 and 7 lbs a piece. The girl usually likes to stay in her bed but will come up and hide under the covers if its chilly out. The boy likes to sleep on my legs. I am a light sleeper and do not move an inch while sleeping, so they are used to snuggling with me for safety as the Ex-Gf and lady friend since then have been more mobile in their sleep. However if I am having a restless night, or start moving about a lot they jump off and go to their respective crates/beds.
About OP's question. I am not a light sleeper but I always feel my cat when I'm asleep with him, it actually wakes me up some enough to not roll onto him.
Or lay my feet on him. But not everyone is like me so good luck.
Cats do bite when squished my grandfather is proof of that.