You would really need to have unnaturally tiny hands to not be able to fit a flex
Check out the following for some options
Also, the xSIID is a good option, and there may be a possibility that an xSIID could be enrolled into your current system, but I would suggest you get yourself a test card to check compatibility first, something like this
I’m assuming you have gone for the xSIID due to the form factor and the blinky 
A NExT or xNT could be another consideration for you, but again get yourself a test card (NTAG216) to test it first.