Two dogs was simple for me!! I have even taken 4 dogs with me on a regular basis and do just fine.
They do have carriers now that are made for two small dogs to go in so they can both go with you everywhere.
I would say that if Lex is well socialized, she will have no problems with you adding a new dog, she will most likely welcome it. Most dogs do better in pairs, after all they are pack animals.
I say if you have the time, money and room, go for it!!
