The back to back double book sounds like an Ace Double. The Ace publishing company (Don Wolheim, editor) published these from the 1950s through the 1970s. Since most Ace doubles had different authors back to back, and this one apparently had the same author on both sides, that narrows it down quite a bit.
The golden skinned aliens sound like the Fuzzys, created by H. Beam Piper in the novel Little Fuzzy and its sequels. And Piper did write for Ace books. But I think the Fuzzy novels were from a different publisher.
You can find a list of all the Ace doubles here: http://en.wikipedia.org/wiki/Ace_Double