yes of course you can
you buy it from a place that sells doors
the one you show has very thin, weedy glazing bars that a boisterous person could crash through if they ran at it. A sturdier one, as used in front doors, where the timber is thicker to keep out burgars, would cost more. You need one with quite small panes, not a 2XG or a 2XGG, where the gap is big enough for a person to climb through.
I have a feeling it might look better in a porch, or just inside a hall or passage.
There wil probably be a door merchant in your town with a good stock and a catalogue. Measure the gap carefully. You will most likely need a door frame (this not very expensive).
Doors are best fitted by a qualified joiner, he will do a better job, much faster, than a general builder of a handyman. Ask around for a recommendation, and he can probably recommend a door and a local supplier. If money is tight you might get a second-hand one from ebay or freegle, or a friendly joiner might have one he has just taken out.
If you are likely to want to remove the door from time to time, have it hung on lift-off hinges. If you want it to automatically close, use rising but hinges.
A joiner can also make you a door or gate to fit.
Remember that a door with holes in it is not secure, as people can reach through to a lock with a key in it, or a nightlatch.
There is a type of lock that you could use, it would cost you £38.50 plus VAT and delivery from the cheapest supplier I know. I will not describe it here as it relies on subterfuge, secrecy and ignorance but I can pm you on request.