A pallet could be a good idea. I used SpeedShift to courier an engine, but not without some issues (which shouldn't apply to seats). When shipping an engine, it's very difficult to ensure that it won't leak oil when laid on one side. The actual company that did the shipping (SpeedShift farm out the work it seems) claimed that they wouldn't deliver due a leak but they delivered it anyway
. They offer a "kerb side" to "kerb side" delivery and may not want to enter any premises to collect or deliver, but the seats aren't heavy and this shouldn't be a problem.
The seats can be laid on their sides on a pallet with some "protection" (bubble wrap? cardboard?) and restraining rope or straps (thin ones should be OK, with my engine one of the straps got broken
and needed to be heavier duty).
Laid on their sides, the height of the seats should qualify as a "half height" or less and therefore be cheaper - but not all pallet shipping companies do that.
And of course you need a pallet...but plenty of them get thrown away (especially at this time of year with Fireworks Night coming up) so you should be able to blag one. I still have one myself (not the one covered in engine oil however).