Welcome to the Forum. I think you will find that TI swimming isn't really about doing specific workouts. It is about learning fundamental skills in this order:
Balance (first and most important)
Propulsion (only after balance and streamline are established)
Then, perfect those skills (a never-ending journey). TI is about becoming as perfect as you can. Speed is a by-product. It comes from skill, not from fitness or "working out."
Have you checked the TI green zone chart? You can find out about it here at Coach Mat's blog
Until you are swimming somewhere in your green zone, I'd suggest that most of your practice be focused on increasing the length of the stroke until you are. It is easiest and most convenient to measure stroke length in a pool, but even in open water you should be able to measure off 20m to do a test to find you SPL (strokes per length) and see if you are in your green zone.
Once you can swim comfortably at a variety of SPLs in your green zone, start using your skills to gain speed. Speed = stroke length x stroke tempo. So you can get faster using a longer stroke, or faster using a faster stroke rate. There is an optimal stroke length and tempo for each event, depending on how fast and how far you want to swim. Having a tempo trainer and a measured distance is a good way to work on increasing your stroke rate while still keeping your SPL within your green zone.
Here's a good discussion from Terry Laughlin, TI's founder, on how to work on improving stroke length
. It will take some creativity to adapt these ideas to open water practice, but it will give you some idea on how TI focuses on improving skills rather than on "working out."
A long complicated non-answer, I know. But mastery is not a simple, "do this workout and you'll get faster" process. Good luck, and enjoy the journey!