Well there are a few options really, but no land rover has been designed with passenger comfort in mind. I'm the same height as you and possess a racing snake 21 stone figure with size 14 clod hoppers. Long trips can be numbing to the nether regions and weirdly, the ankles.... It's a question of how much you love old landies versus how prepared you are to suffer a little discomfort. Don't even consider an 80" series 1. The 88 and 109's are ok for long distance travel.
I agree with Rambo that a smaller steering wheel is a good start. On standard 7.50 tyres there's very little difference in effort to turn the wheel and I ran a series 3 109 diesel on 31/10.50/15's which you just get used to driving like that. You just have to get rolling before turning the wheel. The smaller wheel allows you to fit better, more comfortable(thicker) seats from later land rovers or just about any other car and still get your legs under the wheel. Companies like MUD UK offer diy fit MUD rails to lift the seat base slightly, allowing it to slide further back than standard and/or recline more. This only works if you have a Landy with no bulkhead behind the seats, otherwise chop it out and put a bulkhead removal bar in. BIG increase in comfort and you have more room for the right knee between wheel and door! The station wagon tropical roofs allow less headroom than a standard hard/soft top. Something else to bear in mind is that if you make the driver's seat too high, you continually have to duck to see where you're going under the top of the windscreen frame. Of course it goes without mention that you have to adopt the land rover driving position of elbow out the window to allow you to close the door and sit in front of the steering wheel. None of these mods will please the purists though. I admit to being into old land rovers more than the defenders, but if it's comfort you're after the series landy is not the place to start. :nono: