Working in an untreated room without isolation has left me considering tearing apart my room and rebuilding it from the ground up. I have considering skipping the isolation and only acoustically treating the room, but that won't do much for the lawn mowers, cicadas and thunderstorms I hear almost daily. Tearing the room down to the studs and rebuilding will give me the opportunity to properly isolate the room and then treat it for best results.
I've contacted a few designers, purchased a few books and I've been browsing sites with studio design forums. There's a ton out there I haven't touched yet, but at this point some of the best resources are:
Home Recording Studio Build it Like the Pros (Rod Gervais)
Master Handbook of Acoustics (Everest & Pohlmann)
Handbook of Sound Studio Construction: Rooms for Recording and Listening (Pohlmann)
I am using SketchUp to build my room in the box before I attempt it in the real world. You can either pay for the current version, use the online free only version, or download the legacy free "Make" version (which is what I did) from here.
This is a top down view of what my room currently looks like. As you can see, I don't have the length for bass to fully form, a sliced off corner, a closet, a fan, a window, and luckily some 12ft ceilings.
I also took some measurements so I could get a feel for my current (non-existent) isolation. This was done with an SPL meter, weighted C, slow. The number in blue is the first reading without audio playing in the room, the red number is the reading with a 100db track playing in the room.
There are a few different paths I could take in regards to isolating the room. Of course each has its pros and cons and are priced accordingly. It has been suggested I consider either Iso clips or inside-out detached.