Unfortunately "Simple Delivery" is now compulsory on ebay. Although you can get away without having a printer you need a smartphone to receive the QR code because you'd need to take that to the post office so they can print your label. You won't get the buyer's address without the label.
In theory items worth £10 or less and weighing 100g or less are exempt from Simple Delivery but I'm not sure how that will work in practice.
As a temporary measure do you know someone who can lend you their smartphone to use?