There are tons of cuffs that have the locking option, no padlock necessary. Even though they won't really LOCK, per se, they will stay in place quite well. I do feel that getting a padlock is the best way to go, though. I'm assuming you want leather since metal handcuffs are not usually what people are looking for. However, I recommend anything from Aslan leather or Leatherbeaten. Here are some of the ones that I like:

Jaguar Cuffs
More Jaguar Cuffs

It seems they've actually gotten rid of the majority of my most favorite cuffs, so the only locking ones are the Jaguar cuffs, the suspension cuffs, and the pony hobbles by Sinvention, but those are rather bulky and they may not be what you're looking for. Too bad they got rid of the Luxe cuffs, those were padded and had the locking buckle.

Oh, whoops, nevermind! Here they are: Luxe cuffs. Those are my ABSOLUTE favorite, and you may be able to get away with getting two pairs for both the wrists and ankles.

Hope that this helps!