Hello Siempre and welcome to the club.
Seeing that nobody has replied to your request for info. I thought that you might be getting discouraged before you have started. I don't know that I will be of much help, but here goes.
I had exactly the same problem with my garage door and a Nissan Tino. My wife bought me a stub aerial from Halfords, hence I don't know the make or price, but it solved the problem. It is now ten years old and has replaced the whip aerial on my C-max.
The aerial is 17cm long but because of the angle, it is only 11cm above the roof and as it is fitted at the front on a lower portion of the roof, it is only 7cm above the highest roof point. I hope that this makes sense.
On my car, the aerial works perfectly and actually appears to receive a better signal.
What I would suggest is a visit to your local car spares shop. I am sure that they would let you try it on your car if you are careful with the packaging.