Easy way to add insulation to existing ceiling of small utility room?

[SlinkyDogg]

Our utility room roof is very poorly insulated and thus very cold.
Is there an easy way for me to improve this?
Is there 100mm insulation with a paintable surface on one side that I can glue or screw to the existing ceiling which I believe is some sort of plasterboard.
It's not really visible to visitors and we may renovate the whole kitchen & utility room area in a few years so I don't want to spend a lot of money on it.
Any suggestions appreciated.

bump

Yes you can buy insulated plasterboard, but if you do this you run the risk of causing condensation in the roof void above. The roof void must be well ventilated to minimise condensation. Make sure the insulated plasterboard is taped at the joints and well sealed or install a separate vapour control layer above to help minimise condensation. Condensation in the roof = rotten joists.

You risk interstitial condensation by doing this.

Look up 'cold deck flat roof' for ideas on incorporating ventilation.