first time travelling to Lake Gards, Italy

we are hoping to travel to Lake Garda, Italy next year (I like to start planning in advance!). I am very confused by all the different suggestions on routes, which include the Gotthard Tunnel, Mont Blanc Tunnel and various passes - St Bernard and Simplon to name a few!!! we would also consider travelling from Rotterdam or Zeebrugge instead of from calais as we live in the North of England. We are towing a caravan and would like an easy route which is fairly quick, without too steep hills and would rather pay more for easy route than avoid tolls etc  but end up on small winding roads! Any suggestions/advice would be welcome. We will work out overnight stays after seeing the routes.

Thank you,  Anne