If the speaker pair can be kept five feet apart, with your listening distance also five feet from both, you will get the stereo image from the pair. Anything much less, and the five should give you a decent stereo image with the better midrange.

But...if you can get the units on a returnable basis,  trying both is ideal.

I would personally go with a matching pair of Sonos One’s, particularly as you have one of them already. The Sonos One is great value and an award winning speaker and the stereo separation will make a huge difference to the soundstage and will sound great in a small room, particularly when listening at the ‘sweet spot’. 

hi @firestar I second Ken_Griffiths and would add that if you do not use voice commands you may opt for a Sonos One SL 

Thanks all for your advice! I decided to get a second Sonos one. 
 

i went to the Sonos showroom in town, and can hear the difference between one Sonos five, and two Sonos one, even if the Sonos one pair is not placed 8ft apart. The soundstage of two speakers is clearly a class apart. 
 

Hope to hear the same soundstage after I set it up in my room tonight. 

Where do you get this 8 feet number from? Even placed, for example, 5 feet apart, if you sit approx 5 feet away from them, you will get the soundstage effect. The key is that the two speakers and you should be three corners of a triangle with equal sides. It really does not matter - within limits - what is the length of each side of the triangle.

The TruePlay feature is a good companion to get the soundstage well.