What kind of dog 2 get?

I have a dog already named Roxy. She's about 70pounds. Roxy is also 3 years old. I really want a little lap dog. I also really want a puppy. The only thing is my dog attacks other dogs that come in my house. But when she's other places like (dog parks,Vet's ect.) She loves other dogs. Her vet thinks she would get over her jealousy if we got another dog. But would it be better to get a big dog or an older dog?? Please answer 10points best answer!!!