Chi-spaniel puppy momma here!

Hello all! I have a six month old cocker spaniel - chihuahua puppy! She is super playful and has quite a few tricks under her belt. She also LOVES being around other dogs (and people!). For this reason I feel SO guilty when we have to leave her home alone a few hours a few days a week. I am considering getting a second dog AT SOME POINT. Any advice on this would be great. I have read that I should wait until she is at least a year old, but have also read that introducing a second dog while she is young is also good so that she does not get too used to being an only dog. I'll also mention that I am open to the second dog being either older or younger than her. Any thoughts would be great! Thank you!