Need recommendations for basic(yet solid) PM tool with customer portal.

Context -  I am building a productized service for small agency owners and solopreneurs. Use case -  Once they make the payment/subscribe, they will get a welcome email with a signup/login link to the customer portal to build their profile (agency name, website, country, etc.), upload requests and assets, review the drafts and leave comments.  Current situation -  I have gone through the obvious (and popular) options - monday.com, wrike, and the likes. They either are expensive, high learning curve, or have a minimum number of users cap. Do share your recommendations or comments on how I should go about deciding on one platform.