CRM with simple external user collaboration?

I'm looking for suggestions on a solution for how to collaborate with clients.

1. Currently I use Zoho crm to gather leads through wordpress site.
2. Gmail to email back and forth.
3. Zoho sign to have clients sign contracts.
4. Xero (through accountant) to invoice clients
5. Dropbox to have clients share documents for review

I feel there is a lot of fragmentation and possibly tools that could help me automate more of the process.

Another issue is that I tried to switch to Gdrive since it's part of the google work spaces, but it seems to be a pain for external users (non google users) to share files, unlike dropbox which just works.

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I've tried using zoho workdrive but again it requires the end user to create a zoho account. Clients seem to find it frustrating having to sign up to a service they have never heard of and go through the hassle.

I want a platform that doesn't require the end user to create accounts (preferably). Why is it so hard to get good collaboration software for external users?

Any ideas?