My last major CRM work involving companies and individual contacts was with CiviCRM. We used it at a supply chain trade org (hosting industry events, training people to manage global supply chains with our proprietary certification framework) on a company membership model (at the time, I had to build a module that checked individual's employment status, company membership status, and assigned both CRM and CMS permissions based on that check - they've since integrated that).
It may be (or seem like) a lot for your use case:
It attaches to an existing CMS. The Drupal module version has the most features. On the plus side, there are a lot of Drupal modules you probably won't need to enable, and as of Drupal 8 (v9 was just released) it makes an excellent headless server (REST and JSON:API by default, GraphQL available). How well Civi integrates with that, I'm not sure, as my last major work with it was in Drupal 7. You also benefit not only from Drupal's massive module ecosystem, but also Civi's CMS-independent plugin ecosystem. And you get Views, probably the #1 applauded and copied Drupal feature.
The C in this particular CRM stands for "constituent," not "customer." In my use of Civi, this hasn't been an issue and it did what we needed for customer relations as well. That may be a positive for your use case, or it may not.
It's self-hosted and PHP-/MySQL-based, depending on how you feel about that.
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My last major CRM work involving companies and individual contacts was with CiviCRM. We used it at a supply chain trade org (hosting industry events, training people to manage global supply chains with our proprietary certification framework) on a company membership model (at the time, I had to build a module that checked individual's employment status, company membership status, and assigned both CRM and CMS permissions based on that check - they've since integrated that).
It may be (or seem like) a lot for your use case: