Changing cat from indoor/outdoor to indoor only

Thanks for all the ideas, I will pass them along. Part of the problem is that my brother had been ill and unable to work for some time and SIL is worried that the kitty will be lonesome. I know the cat already misses his presence as bro was a bigtime cat lover. But we have to resist the urge to humanize pets in our minds. My own old cat seems to fill any available hours with sleep or looking out the window. I'll bet this one will do just as well.