If you are "retired" on ill health then I dont think you can effect a new Pension.
To effect a Pension Plan you normally need to have a "source of relevant earnings". An existing pension is not deemed to qualify in this regard.
Yes, you could effect a PRSA, but even here you would not get any tax relief (as you dont have a "source of relevant earnings" against which to offset the PRSA contributions). A source of relevant earnings is generally "earned income" and a pension would not qualify as an income on which a pension could be funded.
And if you wont qualify for tax relief on the contributions then there is no point (since you will eventually be taxed on the income when drawing the pension).
If you want to save then I suggest a regular savings plan.