relay modules?

Hi all. Two separate projects which will need a relay of some sort to run from a Pi or similar.
I'm really looking for something plug-and-go rather than build-your-own (especially item 2 below)
First is a dpdt relay to switch around 12-20 V at a couple of amps. spdt are easy to come by; the only dpdt ones I've found are on aliexpress, but their longevity is possibly open to question :-{
Second is something to switch mains safely - a full 13A to run a 3kW heater. I've drawn a blank: best I can think of is to butcher one of those wireless mains switch modules, which would at least provide a good isolation gap :-)
TIA for any ideas.
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Mike Scott
Harlow, England