Yes, all dentures require a mould of your mouth. Modern dentures are quite light, but older ones ("Vulcanite") early 20th century were heavier. I have also seen some metal ones made in POW camps by inmates made in metal.
Modern dentures rely upon a good seal all around the edges to make a suction seal. If this is not possible (poor bone depth) then people may use denture adhesives to help. Dentures with suction cups were tried once, but they would create damage to the palate and are no longer made.
If you tether dentures to the bone, you still need to be able to remove them for cleaning. It would be otherwise like never taking off your shoes! Conventional implants can be used as a supplement for removable full dentures with O-ring type attachments (full coverage) or fixed (partial coverage, able to clean underneath). Sometimes mini-implants are used for removable dentures - easier to place, but mostly used while waiting for conventional implants.
Ideally you wait 3 months after extractions for the bone to heal and reshape (remodel). "Immediate" dentures can be made to replace your extracted teeth on the day of extracting, but will cost more and require more adjustment visits. Sometimes any bumpy bone is removed to make the fit easier. The bone is the alveolar ridge.