Do you have any suggestions on features other than those antennas that would make her a little sluglike?
The largest change with a SM is 1) Eye change and 2) Facial (notably eyes) colorization.
So my first suggestion would be to slightly alter Tsunade's eyes. Possibly giving her a large blank pupil (like the Byakugan but silver-grey in color).
After that, I'd keep her Byakugou seal released pattern but make it Katsuyu Blue. I'd also add the blue streak (like the one going down her chest) on the backsides of her arm which would go up on the shoulders and have two meeting points: the nape of the neck and then connected to the curving bottom parts of her Byakugou release seal.
I'm personally a fan of the simplier things in design so no extravagant things like DSM horns float this boat lol!
The idea of an eye change plus tatto change is also reminiscent of how Hashirama's is. A nice way to relate them together.