You don't mention the size of your database. Does it fit in memory? If so your disks aren't going to matter a whole lot outside of potentially being i/o bound on the writes. Otherwise getting your data into SSDs absolutely can have a few multiples of performance impact. The NVME M.2 drives can really pump out the data. Maybe push your WAL onto those (as few motherboards have more than two connectors) and use regular SSDs for your data if you have high write rates.
Meanwhile, if you're looking for strong cloud hosting for Postgres but the speed of physical hardware, feel free to contact me as my company does this for some companies who found i/o limits on regular cloud providers to be way too slow for their needs.
good luck (and pardon the crass commercial comments!),
-- Ben Scherrey