Zurich (Aer Lingus and Swiss from Dublin) would be closest to the Swiss side and the western end of the German shore .. for the Eastern end of the German shore Ryanair's "Munich West" (Memmingen) would be a bit closer (closer than it is to Munich proper anyway )
We flew to Friedrichshafen airport a few years back but Ryanair has discontinued this route (terrible pity) and replaced it with Memmingen airport.
Last year we flew to Memmingen airport. You can get a taxi outside this small airport to the train station in Memmingen. From here you can catch a train to the town of Lindau on Lake Constance.
Lindau is beautiful with a good train station that runs along the lakeside to the town of Friedrichshafen where we stayed and a good base.
From here you can take a local bus, stops outside train station that will take you to the chocolate box town of Meersburg and from there you can cross the lake to Konstanz.
I you're staying in Lindau, you can also hire bikes and there is a cycle route along the lake shore all the way across to the Austrian side of the lake (no need for passports).
Lindau itself is actually an island on the lake connected by a bridge to the mainland. You can also hire out motor boats to tour the lake yourself. Or there are organised boat tours of the lake and some of the other islands.
thanks for all the replies. Would Lindau be a good base to stay in - how big is it?? We plan to cycle alot of places and maybe get trains - wont be driving.
Lindau itself is quite small, you certainly don't need a car to get around the island and the train connections are very good.
But, if you are planning say a 2 week holiday in Bavaria, I'd be more inclined to break it up - I think 14 nights in Lindau would be stretching it a bit.
Friedrichshafen (Ryanair) is still showing out of Stanstead. It is on the lake and you can cycle right around or get the ferry from Meersburg to Konstanz. If you want a base for a few days, I'd recommend a suite in Hotel Barbarossa (good value) and a great big dining room with good food. The local trains/buses are very good and the timetable doesn't lie. Geniesze!
You can cross the lake on the ferry to Bregenz for about €9. It has a lovely lakeside walk, they also hold various operatic festivals on their floating stage that sits on the lake. http://www.bregenzerfestspiele.com/en/ The town was disappointing though.
Friedrichshafen is located on the centre of the lakeside, a good base. We stayed at this hotel about 100 yds from the train and bus station and overlooking a park and the lake. http://www.buchhorn.de/ The owner was prepared to drop the price of our stay to match some of the online discounters.