I would say Google Voice is fine. I ported my POTS number to a burner cell and from there to Google Voice (some technical reason for that runaround) and other than having to dump in $10 once to kick it back into function when it hiccuped it has been a free and useful app for years.
I have a number with VOIP.ms, which I use with Softphone app Zoiper5.
I'm going to attempt to transfer my Skype number over. VOIP.ms has a "availability" tool and it indicates its possible to port it.
>To port your Skype Number, please contact your new provider directly. Learn more
Anyone got any recommendations on who to port to?