Waistband holsters aren't necessarily a challenge for seated draw. As noted, crossdraw is one option. However, a strongside, 3:30-4:00 position, 15degree FBI cant allows for a decent seated draw.
A shoulder holster that fits well is ok; one that doesn't fit as well, at least in my case, results in tension headaches from the base of the neck up to mid-scalp.
With either waistband or shoulder carry, I recommend a rig that places spare magazines on the opposite side for a counter-balance.
See if you have any friends or acquaintances who might let you try their rigs, before you buy. Holsters, at least the good ones, can result in a lot of money spent, quickly. Unfortunately, holsters don't tend to hold much resale value, so lots of trial and error gets expensive.