There is a number of recommendations to harden a Hashicorp Vault deployment, but is there a SaaS solution, like CloudBees offers Jenkins to prevent that the hardening should be done manually?
It seems that Hashicorp itself offers an enterprise solution including 24x7 gold support called Hashicorp Vault premium enterprise.
To my knowledge there are no services today that offer Vault SaaS. However, if you're looking for a better UI/UX, there are great options out there for a Vault UI (A full Hashicorp supported list can be found here). I've personally tried out both Cryptr and Goldfish and have found both to be robust and complete.