The best bet is to have a thermal scan done on the house as part of an energy audit.
- This will tell you exactly where the walls are cold and therefore missing insulation.
- This should not cost more than $300-$400 to have done.
Once you have the report, you can get a price from a contractor to drill small holes in the walls of the bedrooms where needed and blow in insulation.
In general, drilling holes at the top of the wall and blowing insulation down is better than trying to do it from below. The holes can be easily patched and repaired to match the existing finishes.
For more information:
Read "We have inadequate wall insulation. What is the best approach to insulate our walls?" a Q&A answered by Michael Holcomb.
Also, check "I want to add wall insulation to my 1920 home. I have two locally available options -- Icynene and Tri-polymer foam. Can you advise me?" a Q&A answered by AlexGeorgiou.