Best practice, if database shapes do not match DB requirements?

Currently on an old X7-2m at an old patch version, but working on a migration to X11-HA, at the latest patch version.

What is best practice/what are other people doing if the available database shapes do not match the requirements of your database? E.G our largest database requires a large SGA and PGA, and needs to support a large processes count. But the Database shapes that would closest match this, would be expecting a very high cpu count, over the number we are actually licensed for.

What we have done in practice is just set a placeholder shape when creating/registering a database, and updating the spfile afterwards. But that has caused a couple of issues when databases have been re-registered and had tins overwritten.