Personally I would say if you have a Partner/Wife they have probably got somone to write and send it.
We did something similar to my Dad years ago when he was a painter decorator and was doing a lot of new build jobs.
My Step Mum decided it would be really funny so I took the card to work got the secretary to write it out and I posted it from Hackney as this was where he was working at the time.
Bless him my Dad was really honest showed my Mum the card and spent about 5 weeks trying to work out who had sent it to him lol