I think it is best to be able to have easy access to both of them which might be better in limited space. Be sure to show simultaneous acceptance and affection to both of them. Here is some info which may help:
Be available as a referee during the first few days till you are comfortable. Showing simultaneous affection by sitting with both dogs, petting and cooing them together reinforces that there is no favorite pet. Feed them separately for the first week or two until the relationship is predictable. Try to keep as many elements of the older dogs routine constant so he feels comfortable that his situation is not in jeopardy.