Successful, mature SaaS companies generally use some sort of hybrid sales model in which they embrace self-service, transactional, and enterprise sales.
Self-service sales, with their lower price points and shorter sales cycles, are a growth strategy unto themselves. What you lose in deal size, you make up for with sheer volume (not to mention upsell opportunities).
To deploy a self-service sales strategy, you need to simplify. Your customer needs to be able to easily find, understand, try, buy, use, and pay for your product.
Towards this end, the key to successful self-service sales is to have fully automated systems to manage customer acquisition, onboarding, billing, payment, and account management. These automated systems eliminate the need for sales support which translates into a lower CAC (customer acquisition cost), relative to the ASP (average selling price) for a new customer.