DH has been at his job for a few years now and is utterly fed up of it, the hours are long and the company used to be quite good to work for but not so much anymore. There are no other roles he could go for within the company.
He has therefore started looking at other jobs, the problem is he doesn't really know what he wants to do and has basically no qualifications and very little previous experience apart from the role he is currently in and he doesn't want the same role at a different company. He is currently paid quite well considering he is basically unskilled.
He has mentioned a couple of jobs which would be a massive step down in salary for him; we have just brought our first home and whilst we aren't struggling we were hoping to start overpaying on our mortgage to enable us to reduce the term, at the current rate we won't be finished paying it until we are nearly 70 
He knows I'm not keen on him taking a job that would mean less money but at the same time he is truly miserable where he is; would I be unreasonable to put a limit on the amount we can afford him to lose?