Hi and welcome!
I have both. The feeling is completely different. There isn’t a 100% equivalent of a bigger Morph I know of, so best write Sensel - the more ask the more likely they might consider it 
That said, having several is a way out. You just cannot e.g. pitch bend across Morphs and you need a USB hub which can be inconvenient and a source of failures. The not-bending-between-Morphs thing can be seen as inherent property though - one may just accept it. The upside is that such a “modular big surface” is quite portable. The downside is the setup time each time before you can start to play…
Have thus put my Morphs on a guitar pedal board - which makes it more heavy but also more plug&play:
From the existing instruments the Soundplane might come closest to a bigger Morph. The wooden surface is also very responsive for percussive stuff (scanning rate is even higher). Don’t know anybody who is using it that way though, but technically you have an xyz-input, so one might create arbitrary overlays for Seaboard, too. No SenselApp/Morph-firmware existing either, so one might have to use e.g. Max or Pure Data etc. to do the programming for your specific overlay. Seaboard afaik only works with Macs though.
Continuum is also in that realm, but haptics are quite different. Technically it’s also xyz, so you could come up with own overlays.
Both Continuum and Soundplane come with default ways to play them though which might be worth exploring first. (Soundplane is grid based, like the Linnstrument and can e.g. be tuned in fourth like a bass guitar, Continuum is by default pitch-in-on-axis like piano, just continuous and two expression axis for y and z.
Seabord is always like a seaboard I think, it might be difficult to repurpose it. If you are looking for a super expressive piano-like experience I would also consider the Osmose. Eagan Matrix (the synth inside it) is very good and it is even closer to a usual piano experience. Pitch bending for more than a semitone is more intuitive on Seaboard though, Osmose is afaik more like an Eigenharp - good for vibrato, less for glissandi etc.
Regarding responsiveness: Percussive stuff is imho better on Morph than on Seaboard - particularly a Morph used without any overlay (e.g. “Continuum-style”) is very responsive. Morph also can create more in-between pitches. Seaboard seems always to quantize to quarternotes. Which honestly isn’t too obvious when playing usual stuff - but might get in your way when you have more avantgarde experiments outside the 12 tone scale in mind.