First of all, if you are on this subreddit already you obviously deeply care about your child, and that is a fantastic support for their future! I highly recommend purchasing a few books on the subject matter, and specifically those geared toward preschoolers; they go much more into depth than anything I have found online and are beyond beneficial. Also I really recommend looking into a speach language pathologist (that has certification in fluency) somewhere near your area that you are able to meet with. Even going 1x per month with yourself and your partner both present can have a major impact! Much of the session is training for the parents rather than the child so even 1 or 2 sessions can be impactful! My son went through the same exact feelings it sounds like as yours, so feel free to pm me if you want to talk!