Why not another yorkie lol as they are around the same size and zoom about everywhere together and u wud not worry about any of them hurting each other
I've 3 yorkies 2 x5lb and a 20lb yes gino is a teapot but very gentle with the tinies lol and a 50lb gsd I've to watch him very closely with the yorkies as he is still a big pup at 1yrs old and he thinks he is a tiny lol a full house but I love it good luck on what u pick