replacing older switches/outlets. House wired 12/2. Breakers with 2 small sw for 15a service. What switches/outlets to use?
Why would you even want that?  Push-in (we call them &quot;backstab&quot;) connections are notoriously unreliable.  They are the direct cause of most &quot;some of the outlets on the circuit went dead&quot; type problems.  Those result in a great deal of wheel-spinning for the novice DIY homeowner, as well as a lengthy &quot;bug hunt&quot;, since it's a 50/50 chance whether it failed at the last good outlet, or the first bad one.   It can take a homeowner a day of tail-chasing just to realize that.
The backstabs rated for multiple sizes of wire (#12 and #14) are even more unreliable, which is why UL revoked their listings.  There is no such thing as a receptacle that takes #12 backstabs.  The remaining backstabs on the market are #14 only.
If you're back-wiring because the wires are too short, that's a Code violation. Wires must come out 3&quot; beyond the surface of the wall and be at least 6&quot; of free length inside the box.  You'd need to pull more cable in from inside the wall, if there's slack; otherwise move the box, replace the cable or extend it with an in-wall splice.
Needless to say, wire length is precious, and you should release or simply twist out the wires out of the old backstabs, NOT snip them off.
If you are not comfortable using the side screws, then step up from the 60 cent outlets to the $2.50 outlets, which provide a scheme many call &quot;screw-and-clamp&quot;.  This allows the screw to be also used as a clamp mechanism to allow back-wiring up to 2 wires under each screw.  GFCI receps also provide this.