How to install python3.7 and create a virtualenv with pip on Ubuntu 18.04?

I don't know if it's best practices or not, but if I also install python3-venv and python3.7-venv then everything works (this is tested on a fresh stock Debian buster docker image):

% sudo apt install python3.7 python3-venv python3.7-venv
% python3.7 -m venv py37-venv
% . py37-venv/bin/activate
(py37-venv) % 

Note that it also installs all of python3.6 needlessly, so I can't exactly say I like it, but at least it does work and doesn't require running an unsigned script the way get-pip.py does.