Help needed regarding addition of Shipping Vendors to DN and SI

I am trying to add custom fields to SI like Ship Via which would tell the transporter through which the material was dispatched. Now the problem is that I would like to have it as a link field.

Now to make it a link field I would need to create a new doctype, I would need your suggestions that whether I should create a new doctype for shipping vendors or could it be done using any current doctype which would only show vendors who are doing shipping for material.

An early response with this post would be highly appreciated.