Postage options?

[nikkie]

What choices are there for sending larger items?
Crisp box size ish?

I'd use Royal Mail standard parcels for that (depending on weight)

What point does it work out cheaper to use someone else?

I've used both Payperdrop (£5.99, uses DHL) and this one (£5.25, uses ParcelForce) for large packages up to about 30kg. Both collect from your door so you don't need to lug your box to the post office, and you can track your parcels online. Either works out cheaper than Royal Mail Parcels for anything over about 1.5kg

royal mail standard parcels (according to dp!)