Try Aurora Store.
It is an alternative frontend to the Play Store.
There you can log in with your google account and download your purchased apps.
If they then work with microG is a second question .
But be aware of this (taken from README on gitlab):
Why would I use my own account? Is it safe?
You can use your own account to download apps purchased by you or to access your wishlist. However, you may want to be careful as Google retains the right to block any account. It might be worth using a dummy account for that reason.
Edit:
I forgot to mention that I do not have any paid app, so this might not work don’t be too enthusiastic .