With most IEM's and I think especially with Dynamic Driver ones like the IT01, the fit is important.
Because we all have different sized/shaped ear canals (sometimes even the right side is different from the left!), so each person will have something that works well for them, but might be a poor fit for others.
The simple best way is to try a variety of different options until you find something that works for you.
The recommendations provided so far all seem good.
Personally, I never seem to get on well with silicone tips. They seem to irritate my ears after a while (an allergy?) and lose the good seal after a while each time.
That aside, the wide-bore tips and wide bore memory foam tips that came with the IT01 are good, and bring out the best in them I found personally.
I also have used Mandarin Symbio tips, a hybrid silicone tip with memory foam under the silicone. A kind of best of both worlds solution, with wide bore size too.
Those have been very good, but after a few months, I'm finding they don't stay in place enough for me and irritate my ears a bit, and I'm looking to switch back to memory foam tips.
I found another two brands that worked well:
1) Crystalline Audio's Crystal Tips (medium or small bore, unfortunately no large bore as yet).
2) Monster Supertips (the foam model, rather than the gel one). Not sure about the bore size; medium I guess?
Hope this helps to add some more ideas into the mix
Does anyone know of a good
wide bore memory foam tip? Since we're on the subject

I'm based in UK, so something from Amazon.co.uk or eBay (UK) ideally, or similar UK based site. But this is not essential.