Looking for some gentle guidance on a thoughtful question from my son about our faith.

Assalamu alaikum. We’re a practicing Muslim family. Last night, during a quiet talk before bed, my 12-year-old son asked me some really deep questions about Allah (SWT). Alhamdulillah, I could answer most to his satisfaction, but one has him seeking more clarity: "How do we know for sure that Allah is the one true God?" I explained about Islam's pure monotheism and the Quran being preserved in its original form, and he said he mostly gets it, but his curiosity remains. I'd be so grateful for any advice on how to gently address this. He fully believes in Allah and is a good Muslim, masha'Allah, he's just thinking deeply. His other questions were: 1. How do we know there is a God? 2. Won't we get bored in Jannah? 3. Where did Allah come from, or is anyone above Him? Here’s how I replied: 1. This one was straightforward, Alhamdulillah. I said the universe couldn't create itself; everything needs a Creator, and He is that Creator. He understood that completely. 2. I explained that Jannah is beyond our worldly understanding-a place of perfect peace with no room for negative feelings like boredom, worry, or sadness. I wanted to add about the ultimate joy of seeing Allah (SWT), but he was satisfied and stopped me there. 3. I reminded him of Surah Al-Ikhlas, and masha'Allah, he knew its meaning! I also gently mentioned that such deep, speculative questions can sometimes be whispers from Shaytan, and we should avoid overthinking. I shared that I had similar thoughts as a child and sometimes still do. The key is to have firm faith that Allah is One, the Most Powerful, with none above Him, and to believe in the unseen-unlike those who demand physical proof to believe. My son is such a good boy, masha'Allah. He constantly reflects on his deeds, seeks knowledge when unsure, and makes choices to earn Allah's pleasure. His sincere questions truly touched my heart, though I tried not to show my concern. Any wise words to help guide his beautiful, questioning mind would be a blessing.