adding more dogs to family

I have an almost 10 year old male Dalmation.We recently adopted a 5 month old female White German Shepherd.She is the dominant Alpha and I think he is depressed.She plays rough.Would adding another dog her age be good now to relieve him of the hiearchal stress?When he dies in a few years,we wanted to get another one anyway.Which sex is the best?It will also be a White German Shepherd.I am trying to prevent the same thing from happening(age difference) and sibling rialvery. I have a small farm and other animals.So this large property is great for dogs.I have had the Dalmation 5 years and he is too laid back for her...She wants all the attention.Maybe a dog her own age would help?

addendum: The local shelter has a female white german shepherd around the same age.Would it be adviseable to add her to the mix?Then they can romp and give my poor Dal a break,plus grow up together and have each othger when he dies.I looked at him before and he has"war wounds from all her rough play.I need an answer quick....should I get a male or female?Or do not get any? She is gloing for clicker training tonight also.