How old is Sophia? Getting a second will be a lot more work...but there are alot of benefits. You should look at this thread - Rachael and Sadie does a great job highlighting the pros and cons of 1 vs. two.
http://www.yorkietalk.com/forums/gen...-have-one.html
Now onto having two. I think it is smart to get one that is the opposite sex and 4 or 5 months old. My Teddy turned a year old in December and in January we got Piper she was a little over 4 months. Opposite sex works great for us. Also, because she was older...she came very socialized. Teddy did not like her very much day 1 -3 but by day 4 they were best buddies and now only a month later they love cuddling. It took me a while to convince my fiance to get a second. But he now admits it was sooo worth it! They really tire each other out and they always have someone to play with
Good Luck!!