I second Seche Vite as the best topcoat, if you can find it. I think they sell it in most Boots. Also, get a basecoat. I don't really have a reccomendation for a good basecoat, though. If anyone else does, please tell me. The one I've got at the moment is pretty crap.
I used to not like basecoats and topcoats because I felt like it made my nail polish too thick and it didn't dry very well and smudged easily. But with practice I've managed to get better at applying thinner coats and now it doesn't feel too thick with a basecoat, two coats of coloured polish and topcoat. Seche Vite makes it dry all the way through, too, which helps.
before you put anything on your nails, wipe them over with a bit of nail polish remover, as this will remove any oils or dirt on your nails that would stop the polish gripping properly. use a thin coat of base coat, so that it's there, but not too thick that it's gloopy. i find its better to do several thin coats, letting them dry completely in between, than one thick coat. always use a top coat, its so much better with one and if you can, reapply it every couple of days.
also, if the nail polish itself is a bit gloopy, put a teensy weensy drop of nail polish remover into the bottle, and shake it up, and that will loosen it up nicely
I had the same problem as you, I spent a fortune on nail varnish and it always chipped off
My aunty is a nail technician so she did a gel manicure for me. The polish was applied on tuesday evening and it's now saturday morning and there is no chipping at all, even at the ends. It's survived constant typing and texting, it's brilliant! Can't recommend it enough.