We have a pellet stove and just love it! This is our fifth year of using it to help heat our home. Our home is 3200sq.ft. and our heat bill(natural gas)was $42 in January of this year. They are very easy to install,maintain and burn! Spend the money ...
you won't stop heat from rising. the farther the stove is from a pathway to the upstairs, the more uniform your whole house temperature will be. your situation seems ideal. install the stove.
A stove and pellets cost more then gas Fix air leaks in house,and have your heating system checked out by trusted repair man (Be safe)