No big deal if mounting bolt holes don't match up
Toilet bases are not "universal"...no pump will fill a different mfr's base. In fact, depending on the age of the old toilet, the mounting bolt pattern for the current version from the same mfr may not match up with old one any more either...So the whole toilet has to come out. Bowls are pretty much interchangeable, so you could buy just a pump/base assembly, but that would cost as least as much as a whole new toilet, if not more...'cuz discount retailer stock complete toilets, but pumps and bases have to be ordered --usually at list price or more. Soyour best option is a complete new toilet. You can prob'ly use at least one of the old holes...Fill the others with with epoxy or other waterproof filler, drill new ones...making sure they're a tight fit for the new toilet's mounting bolts. Set the new toilet down. Touch up any old holes that show with paint or a gelcoat kit. Something else to note: although most toilets are shipped with a straight discharge fitting, most mfrs will swap it out for a '90 for no charge. Depending on where the discharge hose has to go, a 90 can make it a lot easier than trying to bend a hose coming off a straight fitting.