Before you use Boost, Compression, or any mastering tool plugins to increase volume it's worth revisiting EQ on all your tracks and removing any unwanted frequencies.
In particular you want to remove any sub-bass frequencies, so go through each track, solo it, and roll off the as much of the bass frequencies you can without a noticable difference in the sound.
You can also do the same for the high frequencies but to a lesser extent.
You can't normally hear these extra frequencies, but they'll be present in the track. The accumulation of them on all of the tracks won't be audible, but will make the mix will peak with the extra energy there - even though you perceive the volume to be lower.
Once you've removed these unwanted frequencies this you'll likely find you can increase the volume of the whole mix without it peaking, and it should also sound clearer.
You can then apply mastering EQ / compression afterwards to add a bit of glue.