There is only one line in on the Sonos Five, so you’d need to get some sort of physical switch to accept the two inputs and has one output. There are likely several types of these available at Amazon, or your local retail shop.

As for CD players, they’re all pretty much the same from the Sonos perspective, and all of them would have a line level output that the Sonos is looking for. 

Rip your CDs and add them to your local library on Sonos.  

I’d say rip the CDs too, we did that and haven’t had to get a real CD out of the closet for several years. If you don’t have a NAS to store the music on you can make one for around $50 or buy something simple for less than the CD player’s cost.

Second choice would be one of the nicer “pizza tray” CD changers so you’d have five CDs available.

Like this one: https://smile.amazon.com/Sony-CDP-CE500-5-Disc-Changer-Black/dp/B004NQU4YY/ref=sr_1_9

I get the attraction of playing vinyl/using turntables, but there isn't much difference between the experience of playing CDs and listening to the same albums on one of the many streaming services, using their standard and therefore cheapest plans - there is no difference in the heard sound quality for sure. Why bother with even CD rips these days?

A fair number of my CDs aren’t available on the streaming services I have.

When my ISP is having issues I can still play my ripped music.