I noticed you included more detail in response to an answer above regarding your CRM.
The safer alternative is to add a Remote Desktop gateway to your web server environment. This server then acts as a gateway to terminate RDP sessions to whatever computers you have setup. There are lots of other details about that but the gist is simple: setup a gateway, avoid the whole VPN craziness and let clients use the built in terminal service session over a secure 443 session.
Yes it is that simple - although you probably have to do this either via your ISP or your hosting provider.
If doing this by yourself then the chances are the ISP will update to a fixed IP, but your line etc will remain the same and no installation / work is required. So you just wait until the line is set up and ensure it is directed to your server / router / set up.
Depending on what you're after, there are also paid for remote desktop services such as TeamViewer and LogMeIn (although doubtful they will be useful if you need them for a server).