Oh, how I love you Italians Welcome!!!
Giiuseppe, if you cannot find grass-fed beef, don't worry about it. Certainly eat organic all you like. Try getting lean meat (as most of us agree, the toxins the animal ate resides in its fat), but cook it with butter, coconut oil, bacon grease, beef tallow, etc.
You will find many of us have cured multiple gut diseases from going paleo/primal. Search the forums for colitis, and you will find plenty
I would probably steer clear of high fiber, green veggies for now as well. They may be too hard on your gut. Try making bone broth too, and have that on a regular basis.
See you around!