Thanks for all the replies! Reading them was like following my own train of thought back and forward through pluses and minuses
I think for me it all comes down to whether Sammy will like a companion or not. Like I said, other dogs can worry him (would never kill a pup though, he's much too timid and gentle. Plus he has a 2cm overbite and can't get a grip...) but he also has the potential to be really smitten. My friend's Laphund is the love of his life; one day my friend came over without her and Sammy spent the whole time crying at the door and the window trying to find her. I thought then that I NEED to get him a companion. On the other hand, the same friend just recently got a very energetic new puppy and Sammy doesn't like her at all. She is already bigger than him and loves to tease him. I think he's getting used to her though...
Unless I see a perfect solution (e.g. adult female cavalier with a quiet nature who needs a home) within the coming couple of weeks, I think I'll give it another year and aim for next summer instead.
& Samwise (4 year old ruby male)