The original recipe is hardly overloaded with carbs -- about 75 grams of uncooked pasta for six people! (I'd use quite a bit more.)
And I'm with a PP in that I would use Italian sausages, they are meatier but less fatty than English sausagemeat and very tasty.
You can get fennel or chili flavoured ones in good delis or Italian shops in the UK .
Pasta dressed with a sausage and tomato sauce is indeed authentically Italian. And Nigel Slater does a gorgeous pasta sauce made with crumbled sausage, Dijon mustard and crème fraîche.
I'd serve a good salad with the lasagne but follow it with bread, cheeses and fresh fruit.