Bicycle for fat veteran

Hello I am a veteran 76 from vietnam. She wont let me go into the woods like i want to so i think if i get a mountain bike and show her my biking ability then i can go off into the woods. I need a recommendation for a bike for mountain biking that will be easy on the joints with a big seat. The seat has to have some give because my brief will be growing as I go and i dont want it to leak or give me a rash that is very important because if that happens ill just be pissed off and go further into the woods. Any price is fine because i have been saving up for a chance to get out. Thank you for reading and writing on this post