The Toyota Yaris is already an economy car which phenomenal gas mileage, why do you want to get into the trouble of hybrid? If you want to keep the car as long as possible, stick to the non-hybrid models.

Buying a 6 year old car out of warranty is a gamble but is especially so when it comes to hybrids. That said, Toyota makes some of the best hybrid models on the market so you might still be ok. EV Batteries wear out faster in very cold climates, I'm not sure where you are exactly in the EU but that could be something to factor in. I live in California and don't know of many independent hybrid mechanics, it tends to be a dealer niche thing. Unlike traditional gasoline only cars, hybrids will tie in other electronics to the generator so when that goes you're sitting on a dead car until you fork over nearly 5k for a replacement fix. Go with a non-hybrid if you plan on keeping your next car for 5+ years. just my two cents 🧐 

At that age and mileage the batteries should be fine. You really don’t have to be concerned on a Toyota hybrid until they get upper of 130-140k. By 175-200k most hybrid batteries are done. Just have a trusted mechanic look over the vehicle. 

There is only one used hybrid brand I can almost recommend blindly. And that’s Toyota. They are the king of hybrids.

Granted, this assumes everything checks out on the car itself, and that the basic mantainence  schedule was followed. 

More likely than not, the battery will be fine, and go at least until 150K before needing a replacement. And these days it seems longer  

I have a 2004 Prius, with 295K+. And I barely changed the battery after 16+ years at 270K. 

If you are adventurous, you can buy an adapter and use the Dr Prius app to check the battery.