I mainly use Python in Home Assistant and just create a venv and install the relevant application. It’s quite simple that way.
Not knowing what level of Python experience you have I found this primer to be quite informative. https://virtualenv.pypa.io/en/latest/user_guide.html
Not many have successfully managed to get beyond Python 2.7 in HG. Of course Buster is the first release that has Python 3.7 in the repos as standard. It’s virtually impossible to remove Python 2.7 from your install.
Have a look at the contents of the HG Gdebi package installer for clues. You could possibly request that Python 3.7 is included as standard unless there is a good reason not to (refactoring code forward compatibility issues etc).