I have 2 and love it!
Missy was my 1st yorkie, I got her in Sept. of 04 I love her and spoiled her so much for the 1st few months she had all my attention. I wanted another but had the same concerns you have.
I brought Max home the end of Nov 04 and am so glad I did. He has made Missy so happy and filled our house with twice the yorkie love

now I cant imagine not having two.
They play all day and keep eachother busy having fun, then when they need to rest they come sit on my lap or I will hold them. It works out really good, I spoil and baby both of them but when I cant they have eachother to run around with.