Your issue is the time of year. I think you are going this June? late June? There will likely be lots of snow up there until late July or later.
Tours tend to go to either Paradise or Sunrise. Give the amount of snow we've had this year, stick to Paradise which has more for a non-hiker to do. I suspect that Sunrise will have a late opening this year; meaning they will need to push to get the road open by July 4 with too much snow for much hiking. At Paradise, there will likely be 6-10' of snow at that time of year, but, if the weather is clear, you will still have the views of the Mountain. You can tour the Visitor center and the lodge and have lunch at the lodge. The waterfalls will be booming but you won't see any meadows.
Stevens Canyon road (not Stevens Pass as Bill mentioned above), at least to Reflection Lakes is worth the trip. Try to make sure any tour stops there. However, given the time of year and the amount of snow, the lakes may still be mostly snow covered. That road is closed in the winter and they usually try to have it opened by Memorial Day, but this year might be tight if there are any slides on the road.
Do your research now, but wait until you are in Seattle to book. You can check conditions via the web cams at the Mt Rainier NP webpage and also the weather report to see if it is worth your time.
Sue