If 1 channel is enough for you, I'd recommend you the Viofo A119 Mini 2 or the Vantrue S1 Pro. I'd personally lean towards the Viofo. Right on it can be had for 119.99€ on Amazon.de if you use the voucher on the product site. Both have the STARVIS2 sensor which is very good for low light, which helps to even identify license plates of oncoming traffic at night if the conditions are good enough.
The cables can be tucked under the headliner and the A-Pillar trim. If you don't wanna remove the A-Pillar trim because you don't have the tools or you're scared to damage the airbag, then you can just tuck it under your headliner until you reach the A-Pillar, then tuck it into the A-Pillar trim on the top where it meets the headliner to route it to the door gasket. Then I'd just tuck the cable behind/under the door gasket and route it to your fuse box where you can hard-wire it if you want that. Otherwise if you wanna power it using the 12V socket, just route the cable under the dash, make it tidy using zip-ties, tuck it under trims where needed and then have it come up close to the 12V socket. That way you don't actually have to remove any trim, you're not damaging anything, its easy to install and take out again if needed. That's how I route my dashcams in pretty much all my cars. The most important tool you'll need for this is a plastic tool to make yourself some room to tuck the cable in without damaging trim. The Viofo A119 Mini 2 should even come with one.