Room acoustic treatment for dummies

It is not very difficult to find articles about acoustic treatment for various purposes.
I need to decide, what I want to do with my life music:

1. Vocal recording
2. Demo mixing
3. Soundproofing to stop annoying neighbors and require them to be silent during recording sessions

My current setup pretty much is just a 2 channel listening room, and I am almost convinced to do final recordings at a professional studio.
From http://realtraps.com/art_room-setup.htm:
1) "You'll get the flattest low frequency response by sitting 38 percent of the way back in the room"

This is why I can walk between my table and the wall now.

2) "The speakers and listening position should be at the points of an equilateral triangle, and loudspeakers should be aimed at the listener's head in the prime seat."

There is noticeable difference in sound, if I just put my hands behind the ears. Sounds much clearer, as reflections are ruled out. So, bass traps are required (read more on ehomerecordingstudio.com). 

I started my investigation by looking at professional products: 2 options - foam or panel traps.
Ideally I'd need to cover 3 corners in my case: 2 wall corners in the front and wall-ceiling corner in the rear
1) Amazon: 1 panel costs $115. So ~$1k
2) Amazon: $439 - for just 2 pieces seriously?
Or a cheaper version: still, $43 for 4 pieces, I'd need 24 (or more?), but not sure how well those would work.

An even better option is rigid fiberglass: $92.00 + $45.19 shipping for pack of 12

Then I realized that I already have something that can fill the space, namely two folding mattresses like that: Portable-High-Density..lalala...
This is what I have currently as my bass traps for mixing demos
:D >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


After researching all these steps I decided to find a professional studio to record vocals and get final mix done :D