SSH your office's computer with reverse ssh tunnel.

The public computer needs to have GatewayPorts enabled on the /etc/ssh/sshd_config, otherwise it wont work.

Add

GatewayPorts yes

In /etc/ssh/sshd_config

I think the remote option needs to be uppercase for starters. Also this opens up ssh access to your work host to world. You can limit this to localhost on your DO vm with:

sudo ssh -n -R 127.0.0.1:8022:localhost:22 username@your.digitalocean.com

The following command then would be

ssh -o ProxyCommand="ssh username@your.digitalocean.com nc localhost 8022" companyusername@companyofficecomputer

You need netcat installed on the DO host obviously.