Hi Dana, we had this same challenge and wanted to continue to leverage the portfolio functionality. The gotcha around Child Portfolios is that they don't behave like you would expect (the functionality is reasonably simple / basic).
The other big point that needs to be considered is that an investment can be included in the contents of multiple portfolios, so any 'hierarchy' of portfolios needs to be cognisant of that without double / triple / ... multiple ... accounting of an investment.
How we did it was to replicate the portfolio hierarchy with a specific Portfolio OBS for the selected portfolios. Investments could live in each portfolio within a branch, but at the same level across the branches they could only exist once. We built dashboards which extended on the deployed PMO Accelerator 'Portfolio Dashboard' and navigated the drill down within the different "levels" of portfolio via the Portfolio OBS that we had created and then tagged against the selected portfolios. This mimicked the drill down / up capability that we wanted at different levels while still being able to access the individual portfolios for what they could provide OOTB. We got even craftier with the construction by breaking this down by FY as well. There was a bit of work in the approach, including the creation of all the portfolios and the coordination of the synchronisation schedules to spread the impact of the jobs on the Clarity PPM infrastructure (which has caused us failures with the load DW job). The key thing was that we did not use child portfolios to make this happen.