Re: Shikko, toes, ouch!
Some schools include toe warmups in their daily warmup routine: basically you sit cross-legged with one foot up and rub the toes, bend them back and forth, thump the sole of the foot, and roll the ankle. I find that I am less likely to hurt my toes if I do this.
Spending a small amount of time--not long enough to really hurt--every day sitting in toes-up seiza might help too.
Some of our senior people cannot tolerate toes-up position for any length of time. Their aikido is still excellent. So don't give up, even if your toes are never going to love suwari waza.