I would be hesitant to let him look for a chair himself, he'd probably
pick something very expensive and possible inappropriate. This would create
further problems not fix them.
If you call in a chair company you will probably end up purchasing an
expensive chair which may not resolve the situation.
It's very possible that the chair is not at fault, but the chap has
taken the moment to seek attention. Therefore you may be better off requesting
an ergonomic assessment for this chap, which would be objective and independent,
as well as investigating both cognitive and physical demands of this man's
task. Most importantly it will give specific solutions and recommendations,
which will have been explained and agreed to at the time of assessment.
What ever you do you must consider a participative ergonomics approach where
the client becomes an active decision maker in the solutions generated, but not
the sole decision maker, if success is to be achieved and failure avoided.
Regards