However, I don't see in the Watchlist all the topics where I previously posted, but only some of them.

I don't understand why anyone would not use the watchlist. You can configure the watchlist to be exactly the same as "show new replies to your posts" by configuring your posts to be auto-watched and adding your posted-in topics to your watchlist. After this is done, you can unwatch topics that you don't want to see.