Angel, out of the petpets you posted, I'd have to say I like the black Moltenore, the white Anubis, and the white Cobrall best. You say Checkered was hard to match, but I think you did pretty well.
If you're still looking for suggestions, I have some.
I kinda like this pairing, not only for the color and shape, but the description of the petpet, a black Spirkle: "These mischevious petpets roam around on the sea bed looking for bigger Spirkles to be friends with." Since a Jetsam kinda looks like one, and since a show-off-y tough guy would probably like an admirer, I thought, hey, why not...
More black and white and red all ov...er, I mean gray petpets.
Since one of the petpets you were considering was a robot one, I browsed through some of those and picked out a few more. All of these are plain, by the way, no pppb required.
This is a Lyins painted robot, which is a petpet I'm considering for my future Robot Pteri. imho, it goes together pretty nicely with a Jetsam too.
As for petpetpets, well, I'm thinking a Glack or Aboogala would work best, but I'd rather see which petpet you wind up choosing first. There's also a link somewhere in this thread to a page of custom petpetpets that you might want to look at. Or you may decide you don't want one, 'tis totally up to you.
(Hope I didn't complicate things too much.)