I am not sure that I can devote all the necessary time to the creation of a TL (even if this looks like to be interesting). However, i'll help you as much as possible.
I may have found a suitable POD, with very interesting possible futures: everything goes on as per OTL until the death of Bonifacio in 1052. Beatrice of Lorraine remarries in 1054 to the former duke of Lower Lorraine, Godfrey the Bearded (who has been dispossessdof his duchy after the revolt against the emperor Conrad). Around 1066, the heiress to all the Canossa lands, Mathilda, marries Godfrey the Hunchback (an unfortunate nickname), son of first marriage of her stepfather Godfrey the Bearded. In OTL, the marriage was quite a failure. There might have been or not a daughter born in 1071 (Beatrix). In TTL, Mathilda and Godfrey have more luck: Bonifacio is born in 1068, Beatrice in 1071, and Laura in 1072. However, the marriage does not last much longer: Godfrey cannot bear the bossing attitude of his wife, and around 1075 goes back to Lorraine, where succeeds in becoming duke of Lower Lorraine. Except for Mathilda's progeny, all as per OTL. Again similar to OTL are the fights between imperial supporters and papal supporters on the matter of investitures. Henry IV comes to Italy, and has the famous meeting in Canossa on schedule, in 1077. There is a fence mending with the pope, and Mathilda manages to have her son Boniface recognised as heir to Lower Lorraine. In 1080, Henry rebels again against the pope, and descends into Italy again. This time, he bypasses Mathilda's lands, and goes to Rome along the Adraitic road. Contrary to OTL, Mathilda is slightly more successful in her wars (she was successful also in OTL: here things are better). She's not defeated at Volta Mantovana, it's a draw. The revolt of Lucca, her capital in Tuscany, fizzles. Henry appoints his anti-pope, and goes back to Germany.
Mathilda keeps the field: in 1084 routes Henry's italian supporters at Sorbara, in 1085 is again warring in support of Pope Victor. In the meantime, Godfrey the Hunchback dies, and Boniface is crowned duke of Upper Lorraine.
Mathilda marries Welf of Bavaria in 1090, as per OTL. Henry IV once again descends into Italy in 1090, and the final battle is fought in front of the Canossa castle in 1092: Henry defeat is even worse than OTL, and Mathilda gets better conditions of peace: Boniface becomes duke of both Upper and Lower Lorraine, the Canossan county of Mantua is elevate to dukedom, and granted again to Boniface, together with the title of Imperial Vicar in Italy.
In the same treaty, the free city of Pisa mends some fences with Mathilda, and is no more a menace to Lucca nad the Tuscia lands.