Sam2-
Let’s not forget how this thread started. It started with a comment “Can the man that stands next to me in shul and absolutely stinks have a shower. We don’t all have to suffer for your aveilus.”
The implication of that comment is that there is no room to be “stringent”. The comment was shaming anybody who is.
Let’s get it straight. Not taking a shower is not, as you call it, Lifnim MiShuras HaDin. That is the Din. Or as you call it, the Ikkar Din. PERIOD.
There are leniencies which allow certain showering in certain circumstances with certain guidelines. But those are what we call “kullas”. And not all poskim are so happy with them.
So to clarify: There is always Din, Lifnim MiShuras HaDin, and Kullas. Din is not to take any showers. Lifnim MiShuras HaDin may be not to even wash your feet for Shabbos, only hands head and face with cold water and no soap. A Kula might be to take some kind of shower during the week.
Just remember- if you do take your shower during the week, there are rules. Some say only every other day or less frequent than what you are used to. Some say not to wash or immerse the entire body at once; only part by part. You may only stay in the water as little as necessary. And maybe don’t use your best body wash and shampoo that has your favorite fragrance. Remember, you are only allowed to “remove the dirt”, no pleasure is permitted!