"didn't find anything that would be simultaneously very simple to use, quite reliable and providing decent power. "

That is a kind of an engineering paradox which you are expecting.

For more tutorials on Solid State Relays,
start with this link :

http://ecb.omron.com.sg/guide/SolidState_Guide.pdf

And search Omron site for a pdf called "Solid State Relay - Users Guide" It is a nice document that starts wityh the basics and loaded with tips.

Raghu