I think you mean "cooker"
Most are 600mm wide now. Narrower ones will be cramped with large pans. Wider range cookers are available if you need extra ovens. They are very heavy and more work to carry into place and install, and considerably more expensive.
If you get a double oven then the upper small one will probably have a grill in it, which is often more convenient than having it on your only oven.
However a double oven means the main oven is lower so you may need to stoop or crouch. Single ovens often have a drawer underneath for your roasting pans, handy if you are short of space.
I like gas ovens for rice pudding, but a modern fan electric oven is better for regular and accurate heat.
Gas or induction hobs are quicker and nicer than electric rings or ceramic hobs, but any electric hob needs a high-power electrical circuit dedicated to the cooker. If you do not have one, a dual-fuel oven with a gas hob and electric (single, not double) oven will usually connect with a 13Amp plug to an ordinary socket. Or you can get an electrician to install a cooker circuit. It might cost a couple of hundred pounds. If a difficult job, maybe more. You need an electrician who is a member of a Competent Person scheme such as NICIEC.
Some ovens of Italian design have the oven heating element under the floor. They tend to cause burning of the bottoms of cakes and pies. UK design has the elements or burners at the back or sides, or a fan at the back.