Bringing a 2nd dog into the picture ?

We have a 3 year old female bull/mix dog we've had since a puppy - She has basically been spoiled for the last 2 years by my better half. She seems very jealous when the wife and I try to get close to one-another - she will do whatever she has to do to get in between us.

When the wife is watching tv at night, the dog will stay very close by if not already on the couch with her, and should I walk in the room, the dog will pounce on top of the wife, again to get in between us.

The dog also sleeps in the bed with us, however I started that by allowing her to sleep with me when she was a puppy, before my wife was in the picture. Generally my wife goes to bed before I do, and the dog will lay at the foot of the bed. That is of course until I enter the room to go to bed - she will than get up and move to the top of the bed and plop down before I can lay down to get in between us.

So in short, she is spoiled, jealous, and has to be the center of attention in which she will now have to share with another dog. I was wondering if anyone thought it would be a better idea to bring in a male or female dog to add as an addition to our current dog ? She is fixed - just wondering if the transition would be smoother with another female, or a male, or would it matter at all ?

Any thoughts here ?

Thanks

Mike