There is a way of doing this with a single pair of gears, called the Planocentric drive. In this arrangement the shafts are not concentric, as the input shaft is eccentric to the extent of the depth of the gear tooth. The output gear is internal, while the input pinion will have one tooth less than the gear. The pinion is mounted on the input shaft and is separated by a bearing. When the input shaft rotates, the pinion wobbles around the gear at the output speed. This is transmitted to the output shaft through pins. It sounds very complicated, but fulfills the requirement of one pair of gears. You can Google for the images to see how it looks.
Thanks you very much for your suggestions. I am considering all of my options. I will share here whatever configuration I will be using. And if anything troubles me again I will definitely post here & seek your valuable advice. Thanks.
