Darn good advice!
I even do my kokyudosa crosslegged nowadays (talk about learning the difference between hips and center...)
I will add: even more helpful than kneepads is adding additional padding to the dogi pants. I did a how to column on this in the Mirror many years ago - basically you make a couple of huge rectangular patches of cotton fabric to affix inside the pants legs and quilt into them a slightly smaller rectangle of Pellon Fleece. You position it just under where your knees are - you will notice that your pants legs slide up as you kneel so the padding really is needed lower than your knee when you are standing.
I did this back in the days when I still had good knees and it was wonderful for suwariwaza (and also awkward landings from ikkyo) - like pivoting on a potholder!
My best advice for suwari waza is: don't do it. It's just bad for your knees and body. It's one of those things we do because we're told to do it (aka "tradition"), but other than "tempering the spirit through physical punishment" there is little to no martial benefit from training suwari waza that cannot be achieved standing. Mind you, I did a lot of suwariwaza in aikido... I'm just doing less and less of it these days as I try to avoid destroying my body like so many aikido veterans have.
If you must practice suwariwaza, some bits of advice: