Mouse with fewer buttons

I have had to get a new trackball mouse for various reasons I won't go into. The mouse I was using had a lot of function buttons on it, and I had 5 things programmed into it.
 

1. Ctrl-S to Save
2. J and F5, to toggle between the smart tool and scrub tool
3. Square brackets [ ] to toggle between Track View and whatever other view I was using, usually PRV or the Console View.

 
I have come to depend on these being in my mouse hand.
 
Now with this new trackball, I am short one button available to program, as the new one only has 4. Honestly, I can't do without any of those in the mouse hand, without a serious change in my workflow and/or re-training. I'm posting here to get suggestions for a solution. 
 
One idea might be to enable auto-save which renders Ctrl-S less necessary. But also, I'm wondering if there is some sort of toggle option available wherein a single keystroke would either toggle between Track View and PRV/Console, or else one that toggles between Smart Tool and Scrub Tool. Having a single key that acts as a toggle would save me that fifth programmable button.
 
This is the trackball I'll be using, in case anyone wonders.
 
Ideas?

Yes, exactly so. But of course I need left and right click too, so 6 minus those 2 equals 4!