Buy in Germany, staying in Czech Rep. and Schwitzerland

Want to buy iPhone and iMac in Germany, working partly in Schwitzerland, but staying mostly in Czech Rep. Is possible to use support in CR/CHF?

When I want to request a tax refund in Schwitz., buy both apple products in an official apple Germany web side, is it possible? I live on the border with Germany and Austria. With a address for delivery I have no problem ;)

Thanks for answer or recommandation 😊

Zuzana