cash flow chart

[rig9919hd]

I am looking for a way to see how much money my bank account gathers
each month after paying all my bills - including mortgage. I have
searched online and found that the "income/expense chart" report is not
what I should be using because gnucash see's my mortgage bill as
decreasing a liability rather than an expense. The problem is that mucks
up the chart and tells me I am accumulating much more money than I
actually am. I'm pretty sure I can just subtract my mortgage principle
from the "net profit" of the chart (is this correct?). But, I'd like the
chart to show this information.

Also, I read a suggestion that I should be using the "cash flow" report
for this instead. I didn't see an option for a chart on that report. Is
it possible to add a chart on that one?