Hi Saramago,
How about Doepfer A-140 ADSR? Simple but good and inexpensive. Once you build up experience with that one you can decide for yourself what you like to have for your second, third, etc. ADSR.
There are hundreds of envelope modules so difficult to recommend you a right one, therefore I think the Doepfer A-140 is a good start or consider to check the major brands, most of them have at least one envelope.
Kind regards, Garfield Modular.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads