Hi Guido. I found two articles that might help:
Therefore, belief in Jesus is enough to be saved; but you must believe that Jesus is God and flesh; and your belief…carm.org
I think a person either believes in God or doesn't. So, if you believe in Christ and are saved, what more do you need…www.christianitytoday.com
You are right — simple belief is all that’s required, but … that belief must be deeper than just believing a set of facts. The devil is always going to try to trick you into thinking you are not good enough to be saved. Hint — no human is good enough.
I have to say though, and this is my personal experience, that the confidence of salvation is not something the comes immediately. For me it has taken decades for the confidence to really take root.
But for a Christian, repentance is an important part of developing the depth of the relationship with God and Jesus. I think you may be being a little hard on yourself because asking God for the desire this deeper relationship is certainly a step in the right direction. It sounds like you do have a desire to live for Christ :) What I think you might be grappling with is, ok now that I’m saved, how does this thing called discipleship work? And that’s a different journey for everyone.
Does that help?