Just a mini-recommendation for the new AZLA SednaEafit Crystal (regular, non-TWS) tips. I never tried the Xelastics (too many guys I know didn't care for them, so I didn't bother), but took a whirl on the Crystals. From a comfort standpoint with the IE 900, they are dead even, if not slightly ahead, of my previous comfort champ, the Spinfit CP100+.
I don't note any glaring sonic "deficiencies" by my hearing over almost 25 hours of use, but I also haven't done any swapping back and forth yet either to compare against tips like the Acoustine AET07. I did have the immediate sense, however, when first trying the Crystals, that they don't display the brutal clarity of the AET07 (so, actually, this could be a deficiency depending upon one's tastes). The Crystals are a wider bore than the CP100+ so come across much more like the AET07, generally speaking. For those seeking a middle ground, the Crystals could be an option.