maybe a noob question.

I bought a 19 inch frame Hardtail MTB. I mostly ride for fitness and leisure. Have done some commutes as well. I faced some issues while riding long. I started having pains in the palms, and then I discussed with other local bicyclers.

The following was the observations by the local members of the community

1. The seat post cannot be adjusted to my height - seat post was already at the max and one of the members said that it may cause frame breakage on longer rides( I have done max 32km only twice or thrice)
2. I went three times on a 32km ride, and post that had problems with my palms going numb, and didn't ride for more than a week(started riding smaller rides ranging from 8 to 16kms)
3. Frame is too small i.e a 19inch MTB is too small for my height i.e around 6 feet 4 inches, would have to buy a 21 or 22 inch MTB considering my height.

My question is

Can i buy parts such that i can make the 19 inch MTB fit for my height to be ridden.?

One of the members from a local group said the following

1. I can buy a 450mm seat post to increase the height of the seat post and the maximum amount of the seat post will be inside the cycle seat stem.. Hence it would create lesser impact on the frame.
2. I am planning to buy a butterfly bar, an adjustable stem, and also some bar tape to change the handles.

Would these be helpful in making for a more comfortable ride?? Help, observations would be great.

Edit

Cost of the bicycle Rs. 28000 - $400 approx. The cost of the items I am planning to buy are no more than $30.

UPDATE : @Gschenk

Thanks for the inputs, I tried sitting at the front most position on the saddle, this allowed me to be more upright and seems the COM is definitely at the place that you said, I tried varying hand positions as well(Tried narrowing it to over the brake lever more closer to the stem, this gives great relief, and was able to ride longer today :) ).