mandi
dont worry too much about all the bumf they put on the side of the oven cleaning bottles, they have to cover their own arses in case you do something stupid and drink it. its only common sense to wear marigolds and a mask (from any diy store) when handling chemicals in a confined space, just open all the windows and doors and you will be fine.
i spent 17 yrs working in a chemicals laboratory with all sorts of nasty substances and it never did me any harm, in any case having 2 heads is an advantage! (joke, dont panic)
your other alternative is to look in the yellow pages as theres a franchise about where they come out and clean your oven for you top to bottom, why do it yourself when you can pay someone else a few quid to do the dirty work!