Hi Tom - I know what you are saying. We always tell people temperate trees need to live outdoors and have cold dormancy and don't do well indoors. I have a regular (non-bonsai) boxwood in the ground and it survives my zone 6 winters just fine, with frosts and snows and temps into single digits in degrees F. But I looked it up and found this:
Boxwood bonsais may be grown indoors in bright, indirect light, or outdoors in partial or full sun in U.S. Department of Agriculture plant hardiness zones 6 through 9. Outdoor plants should be brought indoors when nighttime temperatures drop below 50 degrees Fahrenheit. In winter, boxwood undergoes dormancy. During this time, the plant should be placed in front of a shuttered window or dim north-facing window and kept cool -- around 50 to 55 F. https://homeguides.sfgate.com/boxwood-bo ... 67823.html
PLACEMENT SPRING & SUMMER
The Japanese Boxwood will thrive indoors in high light and appreciates being kept outdoors in either full or partial sunlight during the spring and summer. When night time temperatures drop below 50 degrees we suggest that you place the tree on a windowsill or on a table in front of one.
Once nightly lows begin approaching the freezing mark, it is time to bring your bonsai inside. During the winter months, the tree should be moved to a northern windowsill where it should be allowed to go semi-dormant. It should not receive any sunlight and should be kept cool (perhaps 50-55 degrees). Water approximately every 7-10 days. After this resting period, it should be placed outdoors; however, once the tree is moved to a location with more light, the watering and feeding schedule should increase accordingly.
Tom knows a lot more about bonsai than I do. At the least, if you continue to keep it indoors, you will probably need to provide supplemental light and misting and then be able to provide a cool area in winter where it can go at least semi-dormant. It will not do well (i.e. likely will die) kept indoors in winter at the temperature rooms are heated to.
Incidentally, yavanna, it might be time to start thinking about what shape you want your bonsai to have. Here's a few examples for inspiration:
https://cultivatorscorner.com/wp-content ... i-tree.jpg
https://assorted4u.files.wordpress.com/2 ... oxwood.jpg
https://www.bonsaiofbrooklyn.com/product ... ges/ki.jpg