When I adopted my first grey, Rowdy, he was a bounce coming from a home he had shared with an IG. He had allot of trouble adjusting to being alone while I worked and about 7 months after I got him I adopted a second. Tracy was also a bounce coming from a home she shared with another grey. Having her in the house really helped Rowdy.
When Rowdy passed Tracy did just fine on her own, it was me that really needed to have a second hound. I have a small townhouse, 1,000 square feet but there is no problem having two big dogs. They just take the couch and I have the chair.
I think it really just depends on the dog and believe that some are perfectly fine being the only dog. Good luck and I'm sure your adoption group will pick the right dog for you.