The idea of "indoor" bonsai is a Western culture thing. There are no "indoor" bonsai in the Japanese tradition. Trees are brought inside TEMPORARILY and displayed in a
Tokoname, but the trees are not permanent residents or interior decor. They are reminders of the natural world OUTSIDE.
There really is no "happy" medium for an indoor tree. Even ficus which are extremely tough, begin to get straggly, leggy and weaker the longer they're kept inside. Ficus really like to have the spring and summer "off" and live outside in full sun to strengthen themselves before they have to struggle through another winter indoors.