Guitar finger picks are nice to resemble long nails. And they are usually pretty smooth so they don't go poking people on the feet or sides. Also very effective against people with ticklish backs.
Dog grooming gloves are great, but a specific one I like, that I've test, and it works better than ones I've tried in the past are these:
https://www.petsmart.com/dog/groomi...-dog-grooming-glove-5270912.html?gad_source=1
It's deadly effective, it's definitely more costly than ones you can get on amazing, but I promise you'll get much more intense reactions from it.
I love getting different hair brushes and using them. Brushes with metal bristles seem to get me great results with oiled feet.
I would say go to Michaels, Joannes, Hobby Lobby and load up on different types of yarn. My toes are one of my death spots and having one of those flossed between my toes is one of the most intense tortures because no matter how much you wiggle your foot or toes, the damn yarn never gets out from between lmao
Electric Toothbrushes are amzing. Would definitely recommend testing a bunch of them out. I think the detachable ones where you can take the brush portion out and just have a metal rod is pretty great, but you also want a certain vibration.
If I haven't made it clear, feet are my favorite spot to tickle, and these are all very effective. For things like armpits and stomach, the guitar nails do really well. Otherwise I usually feel feathers(again, hobby stores are great places to get these) do a great job, depending on the feather. I like the fake colorful ones that are kinda stiff, because the feather itself can be actually felt, and if not you can use the stem.
Sorry that was a very long winded response, but I hope it works for you