A split foyer home is a child of the 1970's raging inflation monster. Note that no new split foyer homes, or split level homes of any kind, are now being built. Split foyer homes were a response to inflation; they were an ultimately unsuccessful attempt to make basements, which are by far the cheapest part of the house to build, seem like usable space.
Not having three bedrooms on one level is also a resale disaster. You would be spending a fortune and, rather than adding value, you would be destroying value.
In general, I would strongly advise against making any kind of improvements, other than cosmetic upgrades and appliance/heating and cooling replacements, to any split foyer or bilevel home. You would be much better off finding another type of home with a master bedroom that either meets your needs, or can be made to do so without destroying value. This means putting in a connecting door to an adjoining small bedroom ( ideally through a closet: buy armoires to make up the storage space), rather than tearing down a wall. This might also be a partial. at least. solution to your needs using your present home, since it would be both inexpensive and still would retain value.
For more good ideas on home improvements that add value, I suggest that you visit the Department of Veterans Affairs Web site and look at their relatively inexpensive home improvement ideas for helping disabled war veterans, since these ideas are also good for the approaching tidal wave of ageing Baby Boomers.