I'm not a fan of TTS files. The voices, tones, and other things are just too distracting for me. So I did some research and found two promising programs that you should look at. The first one is by Amazon called Amazon Polly.
https://aws.amazon.com/polly/ It has a free tier that lets you try things out for a while. It looks from what I saw is that it is similar to programming. I say that because it lets you adjust the speed, tone, pitch volume, and lots more. It probably has a steep learning curve, but they probably used this program (or a better version) to design Alexa.
The next one is by Google.
https://cloud.google.com/text-to-speech/ . It seems to have the same features as Amazon Polly and probably more. However, this one seems more geared to a programming style for voice. I haven't looked to much into it, but from the examples it looks more like a program and more complicated. Google text to speech does have a free tier for a while, but signing up for the services seem to not be as straight forward. The reason is because you get access to a ton of other google apis all at the same time. Wonderful for someone who loves to program, but intimidating when you just want to use one thing.
The only other things I can think of to perhaps improve on text to speech is maybe autotuning the files so it seems to flow better, or to put in background music that takes out some of the awkwardness from text to speech. If it was me I would try Amazon Polly, load up a script you already have made, and then practice with all the different variables until you get something you like. These two programs are probably the best two out there. Especially, if you think about what those two companies have already done with text to speech already. Google has an AI assistant that can book appointments for you and sounds pretty human if you aren't paying attention. I bet Microsoft has an open api for text to speech stuff but I haven't looked into it.
If you need any help with learning either program, I don't mind doing some more research for you. I really do love your files and would be willing to help to get you back into making more files! I do have programming experience.