As @HalD said, I think it’s a little more common to make the deadbolt smart and then use the lockable door knob as the privacy option. Just because of the devices that are available.
But there are some that are available to replace a knob, not a deadbolt. Or you can go with an electric strike.
Most of the smart locks that are not deadbolts are ugly, intended for warehouses or garage doors. Very industrial looking. And have push buttons rather than a touchpad. (Push buttons can be used by people wearing gloves). Schlage has several of these.
Yale recently came out with a more modern looking version in their Assure line. You can get that one with push buttons or with a touchpad.
https://www.yalehome.com/en/products/yale-assure-lock-and-levers/assure-lock/assure-lever-lock/
For any of these to work with smartthings you need to get the Z wave model. (First rule of home automation: the model number matters.)
You also need to measure to make sure there is room below your existing deadbolt.
For discussion of the electric strike option, see the following:
How i made my doors unlock... ON THE CHEAP (under $50) (electric strike)
@rboy is an expert on locks, and may know of something else. 