Thanks all!
To be fair to our old barrow, it has been around for 40+ years, and I think it was second hand when we got it. It has had all the hard years of house and garden renovations, so our new barrow will have a really gentle life.
I just couldn't decide on pneumatic or solid tyres. I wouldn't expect any punctures, and there's a tyre fitting old-style garage a couple of miles away who could (and do) repair punctured barrow tyres, should i get one. I like the idea of a solid tyre type, but think when the ground is soft, the pneumatic will be better at rolling over our lawn.
There's no rough ground, no thorny hedges, so I'm thinking I'm going to go for the largest, pneumatic tyred, galvanised one.
Once again, this forum has proved invaluable, and the the patient, solid advice a measure of why it's such an important resource to me in my retirement. I'd be lost without you guys, thank you.