I live and dive in Libya further south of Malta, I can only use the 3mm suit I have about 3 - 4 months of the year. The rest of the year we use 5 - 7mm or drysuits to be able to dive comfortably and be able to go deeper than 15 feet and do more than one dive in a day. Water temperatures can go down to 16 degrees in the middle of the winter. I would advise a drysuit in addition to the 3mm but if the budge is an issue, then a semi-drysuit will be most appropriate. I did do many dives in the late fall to late spring in 7mm suits but it became very cold when diving below 15 meters and never could finish the second dive in the day comfortably.
Most brand name dive equipment manufacturers are represented in Malta, SP, AL, etc. I have tried suits from all of these manufacturers and have found that SP and AL were of better quality and some of them were very flexible. I would suggest that you start there and check with the local suppliers for these two brands first. I know the names of the distributors for AL and SP in Malta if you need this information.