There is a misunderstanding here. Monism is not the abandonment of dualism but a form of it. Schrodinger points this out when he comments 'As well as the painting there is the canvas on which it is painted'.
The view that only mind exists or only matter exists in usually called monism. However, in order to exist a phenomenon must stand-out from a background and this is two things. It would be logically impossible for only one thing to exist.
Hence subjective idealism is a form of dualism. In order to reject dualism and escape from it we would have to abandon all distinctions and divisions for a doctrine of Unity. The sufi sage Al-Halaj warns us that even the remark 'God is One' is dualism for it implies a separation with the testifier. If we do this then we arrive at Absolute Idealism or 'non-dualism'. In Indian religion and philosophy this is advaita (not-two). The use of the phrase 'not-two' is a careful and deliberate avoidance of any suggestion of Monism, the idea that the world can be reduced to a numerical one. The Unity spoken of in non-dualism is not a numerical quantity and is a rejection of dualism.
Thus mind-only and matter-only theories are not an abandonment of dualism but a lightly disguised form of it. This is indicated by the fact that neither idea works and few philosophers see either as being a solution. The Mind-Matter problem persists precisely because it is not easy to transcend dualism. It would be no solution to reify one and de-reify the other.
The only way to move on from dualism is non-dualism. This allows us to transcend the subject-object distinction and all division, distinction, number and form for a doctrine of Unity.
Thus Russell, a neutral monist, is opposed the views of Bradley, an Absolute Idealist, and while the former declares metaphysics incomprehensible the latter explains it. This is because Russell's 'monism' is in fact dualism, as it rather obvious given that it requires a multiplicity of neutral phenomena.
This debate is old and well-rehearsed. It is not necessary to follow it. If we try to do so we discover we cannot conceive of an Ultimate that is one thing since in order to do so we must conceive of a second thing. For materialism these two things are often Atoms and Void, for idealism it might be mind and mental events.
The distinction between monism and non-dualism becomes more clear when we consider that subjective idealism uses ordinary language while non-dualism requires a language of contradiction and paradox. So different are they that they cannot share a language.
Another way to reveal the problem of monism is to ask whether it falls foul of Russell's paradox. We find that problems of self-reference prevent us from 'axiomatising' set-theory on a monistic single set, just as we are prevented from doing so in metaphysics. The logic just doesn't work. To overcome this problem we would have to abandon mind-only and matter-only theories. Russell agreed that his colleague Spencer-Brown solved this problem in his book Laws of Form by the use of a calculus modelling the non-dual description of Reality and endorsing Absolute or Transcendental Idealism. His own monism ran smack into his own paradox and this would be why he couldn't axiomatise set-theory or metaphysics.
In summary, subjective idealism does not require a different language and is merely the mirror-image of materialistic monism, bringing with it the same terminal problems. Non-dualism is the complete rejection of dualism and it requires a non-ordinary technical language that is easy to spot. This is why the literature of mysticism is so often seen as paradoxical and, by those like Russell who do not investigate it, so often judged to be 'irrational' or uninterpretable. It is because it is not endorsing dualism.
If we want to do our own research we only need attempt to imagine that only one thing or substance exists. It cannot be done. The set of all sets cannot contain itself. Monism, like explicit dualism, must be either incomplete (non-reductive) or inconsistent (absurd). This would be why metaphysics is difficult. If dualism or monism worked it would be a whole lot easier.