As somebody who has recently finished a from-scratch soundproofed studio build, I was strongly suggest that, unless you are willing and able to commit resources fully, spend the money on items like Bermuda mentioned. Soundproofing is incredibly difficult and expensive to do properly, especially on a room that is attached to a bigger structure, as in the case of an office room in a house.
A few key points:
1. Do NOT confuse acoustic treatment like foam tiles, corner wedges, or heavy blankets, with soundproofing. These items reduce echo and reverb within the room, but do NOTHING for reducing volume escaping the room.
2. The single most effective way to soundproof a room within a house is to build a fully isolated stud room within the room, with an inch or so air gap all the way around.
3. Cheap solutions do not work.
With these points in mind, I would reiterate, spend the money on the low volume drum heads, rubber mute pads, or a mesh kit.
For your reference, here's the vLog documenting the construction process of my studio. As you can see, all of this effort, and the result is good soundproofing, but still not 100% silent. This is in a purpose built, free standing room 30 feet from the house:
https://www.youtube.com/playlist?list=PLiIBi-86_El-8XiX0aCjTt6jWJvuGykpM