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My father has similar mobility / fatigue issues. When he is fit enough to stand for extended periods, his 200 mm Meade SCT is fine (he takes frequent "rest breaks" in a camping chair while we move to a new target), but he has great difficulty with it when he gets fatigued.
One option for your friend might be an adjustable observer's chair? (They aren't suitable for my father, as he can become quite unstable when he is fatigued.)
He does much better with my 90 mm Mak on a conventional lightweight Alt-Az tripod, which we can get much lower to the ground than the big SCT's "Field Tripod". We set it up with the Alt axis a little bit higher than eye level when he is sitting down, and he sits in a folding camping chair.
The Mak is mounted at the rear of the OTA, so the eyepiece doesn't change height much as you swing from the horizon to the zenith. He sits side-on to the side of the scope, rather than directly behind it. For objects near the zenith, the eyepiece is oriented almost vertically up and he just needs to peer straight down into it. For objects lower in the sky (where the eyepiece rises a bit higher), he twists the diagonal to a more horizontal orientation, and looks in from the side. When he gets everything set up well, he hardly has to adjust the chair, except when pointing to a different direction.
We've tried setting the 200 mm SCT up in a similar low-set configuration, but the spread of the big Field Tripod legs makes it pretty much impossible to get a camping chair in close enough to the eyepiece. (We can get a little stool in, but this doesn't give him enough support and comfort.) A smaller SCT (100 mm - 150 mm say) that can go on a lighter-weight tripod might be an option?
A similar approach would probably work with a short-tube refractor, but these are typically mounted near the mid-point of the OTA, so the eyepiece will rise and fall further as you move from the horizon to the zenith, and you might need to adjust your seating more often.
Hope this helps!
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