I would suggest my Benchmade 480-1 Shoki, a proper 'Gent's knife' in size and certainly in looks and construction - except for it's no longer available. It opens so easily that it is sold with a pocket carry (Remove the clip!) sheath. Still, carbon fiber scales, m390 steel, fancy hardware and backspacer make it a handsome pocket utility knife. I also have the BM Megumi 482, although it is a bit more difficult to open unless you use both hands. It has cocobolo wood and carbon fiber scales and an S30V blade. It won't likely open in your pocket, so it doesn't come with a sheath. Both are handsome knives with a push button liner lock.
In a larger knife, consider the Spyderco Native5 G10 C41G5. It's lockback blade of S35VN steel has a large thumbhole for easy deployment. It is a handsome and current knife, although often out of stock due to it's popularity. All of these knives thus far have had blades of 3" or less. My last suggestion is the largest - and I must go on memory re it's assist feature, as I removed it when I got home with it! It is the Zero Tolerance 0770CF, or the 0770 with carbon fiber scales and an excellent ElMax ~3.25" assisted opening blade. You start the blade moving by your second hand or pushing the flipper, the compressed spring assists the opening from there.
I am 66 and have CTS and arthritis so I am somewhat 'sensitive' to the OP's friend's problems. All of my suggestions are/were available for $200 or less from the usual forum supporting vendors - and some from Amazon, even. I'd check local sources first. The BM 480-1 will take some searching, however.
Stainz