Using the open source firmware (QMK) that comes with most custom keyboard PCBs you can set keys to act as modifier keys when held or tapped. I set my capslock up like this so that when I hold it down h,j,k,l become my arrow keys and y and o become my home and end keys respectively.

Some PCBs support a split space bar too so if you tend to hit space with one hand the other can be used for a modifier and the home row can house all your commonly typed symbols which are normally out of reach.