Domain redirection to Google Sites

I have been struggling with this for a while now and as it seems that I run out of options I'll try to post a question here and see if anyone else can help

I have several Google Sites, and I managed to have them using custom domain names registered on other providers - an example is https://www.bestalumni.net/

I am struggling though to set up this feature with OVH.
there are some guides like the one on Steegle, that are quite explanatory, the issue is that OVH doesn't allow a CNAME to exist on a certain domain at the same time as other records. I have tried putting all kind of records to try avoid his issue, unsuccessfully. I'm using this domain to run my tests - tundersbay dot com -- but have more to sort out eventually.
I have also tried to remove all records and put only the CNAME one, but still I had no luck on making it work. In addition to doing this, it wouldn't allow me to insert the MX records in order to use OVH mail redirection services.

Anyone who has successfully solved this issue? Cheers.