My Lola is a 1 1/2 yr. old Shih Tzu / Maltese rescue that I've had for a year. I just found my senior Yorkie, Lucy, a few months ago. They get along, and are company for each other, but Lola is a teapot, and is so much bigger. She can be bouncy, rough and too full of puppy play for little tiny, old gal Lucy. One nice thing is the new dog will learn the ropes from the established dog, so the second dog usually adjusts a bit faster. They can also learn the first dog's bad habbits, like begging.
. Travel is more awkward, but I do it all the time. It does take some planning though.