I would argue there are some services that need 5 nines (or more) of availability.
Your support ticketing system and company web presence are two I can think of. I provide the ticketing service myself but I outsource my web presence (the landing page not the app) to a third party service. My thought is the web site should never go down. If the ticketing system is down it means things are beyond hosed :)
Perhaps part of the answer is that if you're a solo founder who is staying solo, try not to create a business where you have these kinds of dynamics.
OR, if you are creating one that does, scale up past being solo ASAP.