You can certainly do as advised above and use ply but remember that each layer raises the FFL and can trap appliances if you are doing a retro-fit floor. You are already, of course, using a laminate underlayment.
After placing your laminate underlayment, why not simply lay the laminate the same way as the floor boards and see how it goes? You can always take the laminate back up and re-fix after putting down ply. After all, you are only working in a small floor area.
There's a laminate knowledgeable floor layer called dazlight who comes on this forum - perhaps he could advise best?
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