Compression In Postgresql 9.6

Hello,

Need inputs on below:

We are working on a setting up a new highly transactional (tps 100k) OLTP
system for payments using blockchain and postgresql 9.6 as DB on Rhel 7.6.
Postgres version is 9.6 and not latest because of specs of blockchain
component.

There is a requirement for data compression on DB level. Please provide
your inputs on how this can be best achieved.

Checked in-build Toast, it compressed the data provided exceed the 2kb
pagesize? If the data values are small and even if there are billion
records they wont be compressed, this is what I understood.

Are there any suggestions of compressing older data irrespective of row
size transparently?

Thanks.