Most Couriers will supply plastic wallets especially UPS who do no end of boxes etc.
Im with parcelforce who supply the plastic wallets but I normally use 4 labels to a page sticky labels from e… very cheap and works straight out the laser printer with most couriers label sizes.
If you want to get very professional you can go with the thermal label printers lots of UPS ones on second hand sites, again most supply rolls of labels for these just not the machine itself unless your spending £k’s
With all the current fuss about single use plastics you would be doing yourself a disservice to add plastic wallets to your packing. Customers are getting sensitive and notice this kind of thing.
Self adhesive paper labels are perfectly professional.