Do you have a diagnosable *speech* disorder, involving dysarthria or hypophonia or hyper or hyponasality or something like that, or do you have a *language* problem?
If you have a speech disorder, I can't see a book doing anything for you. ST is the way to go. I've never been a patient, but I've worked professionally with them as colleagues a lot (particularly in the context of kids with craniofacial anomalies, who almost always do ST). They can help you understand what exactly is going on with your speech and how you can adapt yourself to improve the understandability and the quality of tone, and probably any ST that you find easy to work with interpersonally or professionally is great.
If you have a primarily *language* disorder -- meaning you can pronounce most words just fine and make the normal range of pitches, tones, volumes, etc, but you have difficulty putting together content and expressing yourself, then fewer people in this area are skilled in that kind of intervention. You probably want to work with a speech and language center or communicative disorders center that specializes in acquired brain injuries -- they do this kind of work commonly with stroke patients and also sometimes with TBI patients. These centers also work with people with dyslexias, although ideally if you can find one that deals with acquired rather than developmental problems, it would be better, since that's the boat you fall into. An eval by a school psychologist or neuropsychologist might also be good if you have not had one to understand specifically what your language disorder consists of.
Does the difference between a speech disorder and a language disorder make any sense to you? Since you say you have problems with writing too, it doesn't really sound like a speech disorder, unless you mean two (or more) separate things.