Welcome to the forum. While there are trees that can, with varying degrees of success, be managed as indoor bonsai, Juniper is near, or perhaps even at, the bottom of the list in terms of suitability. It's not just lighting, which would need to be exceptional, it's humidity which is very low in most homes. And then there is the issue of the required dormancy period. Junipers just don't adapt well to indoor culture, sorry. Search for 'indoor Juniper' and you will see that many have tried and it inevitably ends badly. This is an outdoor tree.
If you are unable to keep it outside you might as well give it away to a friend who can, even if that means planting it out as a landscape plant. There are other species that are more suited to indoor culture and we will be happy to make suggestions if you like. It sounds as if some form of supplemental lighting is going to be required, so that should probably be in place before you get another plant.