How do people handle data processing agreements with small, sometimes one-person, suppliers? Do you use a standard 'template' style contract?

The person who dealt with GDPR in our organisation left around 18 months ago and since then things have been in limbo with various competing interpretations of what is required/acceptable. 

We're currently reviewing paperwork and have several small suppliers who get provided with clients data and there's some discussion over what is sufficient paperwork to satisfy the need for a data processing agreement. e.g. in one instance there's an email from an electrician stating they delete our client's data once the job has been completed, for another there is just a copy of the suppliers (5 year old) privacy policy. Are these sufficient? Internally, some think yes, some think no.

How do you handle instances where the data processor is a sole trader/not familiar with GDPR?