Good point rrh. I would think the stern would be a better place for a boarding ladder rather than amidships on a 27' boat. With a heavy man, like the OP states that he is, the vessel is going to heel quite a bit once he raises his weight out of the water making for an awkward angle to climb back onboard. The addition of a Lifesling may be a good supplement if there was an available person to assist you in climbing back on too.
I would further suggest that you seek out some local boat owners that might be willing to let you try their ladders and see what works best for you before you invest in something. Perhaps an even better investment regarding your concern of getting back on the boat if you should go over while sailing, would be to buy a harness/tether system and use it. If one prevents falling overboard, then there is no need to reboard. I see you list WA in your homeport. I am spoiled with the local water temps but I would imagine the shock of the water temperature where you live would sap one's strength quickly. Stay on the boat!!!!!
At the marina I would install a permanent dock ladder . Your neighbors may even want to pool funds as one ladder could be used for a group of slips. Of course, any marina alteration should be approved by your dockmaster. In fact, if a few of you bring up the potential liability, maybe the marina will install some ladders.
You want no one to suggest you lose weight, OK. How about you just learn to walk on water then? :>)