20 week plan HIM again?

What's your background?  Training history?  What did your training look like over the back half of the HIM plan?  What can you do 'comfortably' during a week of training now?

A basic idea would be to start at that 'comfortable' week now and try to gradually add training stress (volume and/or intensity, though likely a focus on volume/frequency) over the next couple months.  Without knowing much, my guess is you should be thinking about trying to swim 3x per week, biking 2-4x per week, and running 3-5x per week.  Most swims should be focused on a main set (using repeats of 50s, 100s, etc.) that includes some relatively hard swimming.  Most of your running should be easy.  You bike efforts should be as hard as you can manage without impacting the rest of your training (ie, don't go so hard that you have to skip a run or swim).   Then you can do a 'race specific' plan over the last 8-12 weeks.  It will be easier to decide what that should look like as you get though the next couple months of training.

If you want to do much better, you really should consider swimming more (not sure what your constraints are, though).  That's also where it makes the most sense to increase intensity--non-weight bearing, low impact, etc--but do so in a gradual fashion (especially if you have form issues to work on, as well).  Weight training is not going to help meaningfully and I would only look to add it if there was no way for you to do something else in its place.