Need advice with solution

[Armen Gasparyan]

Hello, 

Guys I need an advice. I am not an SQL geek but have some experience with MySQL. So Currently I am stuck with choosing the best solution. So I need an advice from proffesionals who really had hands on experience with their solution. 
We have the following situation. 
There is a PHP web application which uses and keep a lot of data in several mysql servers. 
8 Mysql servers are keeping application settings and 1 MySql server keeps database with user accounts and data with information where is user app data stored (including which of 8 sql servers have current users app information). 
So when new user registered he/she get 2 information schemas - 1 on the accounting mysql server and the second one on the app mysql sever. 
Previously these SQL servers were hosted on Google Cloud SQL - it had limitation for schemas (not more than 10000 schemas per one server) so that's why we had such weird quantity of servers. 
Besides we had a lot of problems with dead-locks with Google cloud solution so we decided to migrate to simple VM hosted mysql servers very quick. 
Everything is working fine now. 
Each MySql 5.7 server now has master-(read-only)slave configuration. 
Now I am planning to merge smoothly all these application MySql servers to one Percona 8.0 MySql server. 
This server must have an High-Availabily (this is number 1 priority) with possibility to be scaled further on other datacenters. 
Now I see 3 solutions 

1. Master - Master replication with HA Proxy - second master is not planned for write operations - it's planned just for automated switching in case of 1st master failure. Further scaling will happen with read-only replicas
2. Percona XtraDB Cluster implementation 
3. Galera Cluster implementaton 

Which solution is the best taking into account a high reliability as the first priority?