Thanks for the suggestion, Charlotte.
Great news, we’ve been able to add the total weight of the order to the top of the delivery section on the right-hand-side of the main order page 
The weight should already be shown on delivery notes and can be added to sales orders & invoices by modifying the invoice template, if needed. However, to be honest, we recommend avoiding making custom templates unless it’s important, as you’ll lose out on automatic template updates by us (e.g. we recently updated it for the new draught duty relief regulations), so this is up to you.
I hope this is helpful 