I have a personal rule about not mixing narrative sentences and dialogue sentences in the same paragraph. I also do not like single sentence paragraphs, so on occasion I will violate my rule and combine the two types of sentences in a single paragraph.
I have noticed some authors frequently combine the two types of sentences in a paragraph. I have also noted that some authors combine narrative sentences and dialog sentences spoken by different speakers in one paragraph.
I'm curious about what other authors think of the above.