Which airline are you flying with as their website is where you should be able to obtain their regulations.

barrhead travel

Barrhead Travel would be the name of the travel agent. You need the name of the airline.

luci

oh sorry, I missread.
Flying with Spanair. Checked their site and cant see anything about single suitcases. Will maybe just take one each to be on the safe side.

usual weight for cases is 20kgs each if you use one the weight will be more and classed as heavy not overweight. Check your tickets.

Have just returned and we were given 20 kilos pp, 2 of us for 2 weeks (so had 2 small cases). My sister who joined us for our 2nd week was also given the same allowance but as they were there for only 1 week, took one large case which weighed 31 kilos - the baggage handlers will not touch any luggage that weighs above 32 kilos.