You can upgrade to a Raritan PHC, which has the same pump as the PH II
http://www.raritaneng.com/products/toilets/manual/ph_2.html but on a compact base and with a shorter handle, to fit in the same space as a compact.
The PH II and PHC use the same bowl as your HeadMate. So all you need to buy is the pump and base (part # PHCLBA). You'd prob'ly have to clean up the bowl, but you'll save about $!00 compared to the price of a complete PHC and save a BUNCH in shipping 'cuz bowls are heavy!
The PH II has been rated the best toilet < $500 for at least a couple of decades...average lifespan is about 20 years with just minimal maintenance. A lot of others here have bought 'em will tell you they LOVE it!
Almost all toilets use a bowl that has a 4-bolt mounting pattern, so anyone interested in upgrading to the full size PH II can also do so by buying only the "lower base assembly (part # PHIILBA). The sbo.com chandlery's price for it is $269...the PHCLBA is a bit less.
Otoh, Snuffy...a new HeadMate would be a "plug and play" drop in that should fit the same mounting bolt pattern...but you'd be settling for a much lower quality toilet to save very little money and elbow grease. Whichever toilet you choose, PLEASE read and follow the installation instructions, especially the instructions pertaining to a vented loop in the intake.
Btw...you said the hoses are old. Old hoses become very hard, dry and brittle...prone to cracking, leaking and even slipping off fittings. You'd be VERY wise replace 'em when you replace the toilet. Yes, I know you want to minimize the amount of work needed to get the boat ready to enjoy on the water...but a little extra work now will prevent a lot more down time and expense for repairs later. Prevention is always cheaper and easier than cure.