I’ll just put my preference out there since no one strongly endorsed it yet - get a drop bar road bike! No need for it to be less comfortable than a hybrid or mountain bike. Just get one that fits you now comfortably and hopefully they can help you get one that will still fit you once you lose some weight/become more fit +/or more limber. The drop bars give you more hand positions to alternate between. This greatly improves hand comfort. The lack of shocks of any kind makes for a more efficient, lighter bike. Less fatiguing I would think as your energy is being channeled into forward movement.

You up can still get low gears on a drop bar road bike. I love triple crank options and you can still find a few new triples (Sora or Tiagra) on stock road bikes. You can also go used and find some sweet deals in 105, or Ultegra triple group bikes that others are rejecting.

As as for the saddle, I would say stray away from sprung options. The idea is not to sit on it so much as perch on it. Standing out of the saddle to coast with straightened legs at the 3 o’clock and 9 o’clock position every so often can work wonders to revive a sore butt.

Don’t give up. You have a definite challenge ahead of you with your difficult local terrain. At least you have identified the route that you wish to own - you know about gearing already so what’s next? It might also be worth mentioning the importance of practicing climbing on a regular basis. Deep breathing - like yoga breathing while climbing produces relaxation and lowers the heart rate. Rhythmic climbing alternating brief standing episodes with calm seated episodes helps to.

Also, you are using clipless pedals, yes? Just checking because if you’re not then you are stacking the deck in favor of being less successful. Good luck!