I carry appendix. I have for about 26 years now. I am sure I will be having the whole - shirt tail in the trigger guard catastrophe any day now. or maybe not. I actually tried to get my weapon to dry fire in my pants (after clearing it multiple times). Did the experiment WITHOUT a holster (the way I carried for YEARS). I fed my shirt tail through the trigger guard, shoved it back into my waistband. I also operate the trigger from the outisde. I was finally able to do it but it was extremely difficult. Eventually what worked was - placing my thumb along the backstrap of the pistol and pushing my index finger through my jeans and into the trigger guard (finger outside pants, gun inside, denim wrapped finger in trigger guard). It took A LOT of work. It can be done. Keep in mind - this was a G23 with a 3.5# connector, polished surfaces (the "25 cent trigger job") and the "second hole" mod in the trigger bar to reduce take up. It still required intention and effort to drop that striker. YMMV.
OP =
like others say, kinda depends how big the knife is and how fast you think you're gonna need it. I like IWB 3:30 OR just open carry vertically at 3:00 with a little drop. I notice you say you don't have a carry gun yet. I absolutely love fixed blades BUT....... once you start carrying a pistol, a spare mag, a flashlight, etc you might find folders can be REALLY handy. The more gear I started carrying, the less I seemed to lug a FB.