What other birds can be kept with a budgie?

I had 2 budgies, for a little under 2 years. Don't know their ages or prior history, except that they had nowhere else to go. I didn't want them but they were homeless so I took them in. They grew on me. I now know that their cage was too small, about 18 x12 x15 or thereabouts. It's probably more of a carrying cage. One of them died this morning. She was on the floor of the cage panting, maybe she had a heart attack. I want to send the male away if I find someone with an aviary. I don't have any room here to build an aviary, but my kids don't want him to go. So beside other budgies, what kind of bird friends could he live happily with, and how much space does he need? I want what's best for him, but if I can keep him properly here I want to try. Thanks for your answers guys. Peace.