Condensers are very good at picking up room noise, dynamics work better in less than idea situations. You can try putting your back to the wall, make sure there is a good deal of space between you and any surfaces that you are facing which are likely to reflect audio, that and turning down the gain and getting closer to the mic may be enough.

Since it is just your voice you can look at a spectrum analyzer to get the frequency range of your voice, look at the big peaks and search for sound treatments suited to that frequency range. This will make it much easier on you, treating a room for a small frequency range is much simpler than it is for the entire spectrum.

In terms of where to put panels, breaking up the large flat areas of wall is the first thing to try. Positioning matters.

You could glue the acoustic foam onto a board, add a rail for drapes etc - and then be able to move the whole assembly around to try different positions.