I have to admit I think you posted this last year and I haven't used one since, because we have wheat bags (cherry stone bags BTW don't have the smell, and work fine - they smell nicer than rubber hot water bottles as well.)
But
two years? Since when has that been the advice? I am sure we used the same ones for decades running. My grandparents would always give us hot water bottles when we went to stay and I can't imagine they were buying new ones every two years. It seems incredibly wasteful to throw them out.
We always did boiling water if you had a cover on the bottle, or hot-tap water if it was an uncovered one. There were warnings on them saying not to use boiling water but my mum reckoned it was to do with scalding yourself when filling it and just to be careful.
The only thing I miss about the hot water bottle is the feeling of it - there is something about the pressure of water and the shape of it which isn't replicated with a bag. I don't think the cherry stones stay hot for as long either.