OTL Konrad of Mazovia was mindless brute known for invitation of Teutonic Knights to Chełmno Land, which became nucleus of future Teutonic Order State (as result Konrad is often blamed not only for later wars between Poland and Teutonic Order but also for Partitions and ww2
). ITTL Konrad's father, Casimir the Just, would have a bit different descendants-three surviving sons, born around 1182, 1184, 1187 (Odon, Leszek, Konrad). Odon would take place of OTL Leszek the White and would be Duke of Cracow, Leszek would take Mazovia, while TTL Konrad would follow example of his uncle Henry of Sandomierz and would visit Holy Land. Konrad would join forces of Hungarian King Andrew II during Fifth Crusade. After returning from Crusade, Konrad would settle in Mazovia, where he would help his older brother fight pagan Prussians. Now serious changes begin. Neither Leszek nor TTL Konrad are as cruel like OTL Konrad, who IOTL ordered to brutally execute voivode Krystyn "shield of Mazovia", who was commander of defense of Mazovia's northern border. So Mazovia have less problems with Prussian raids. That is one thing. Another change is the fact, that being in Holy Land, Konrad has seen how knightly orders work, knowing also what happened in Hungary, where Teutonic Knights tried to carve up their own state but were expelled by King Andrew II, Konrad would advise his brother to not repeat Andrew's mistake and to not invite Knights. TTL Leszek would die childless in 1225, leaving Mazovia to Konrad. Konrad would live until old age and would never even think about bringing Teutonic Order to his land. So how would situation develop? Teutonic Order (or other Order from Germany) could still expand into Prussia like they did in Livonia, starting from Baltic Coast, but conquest of Prussia would not be easy, Baltic Prussians were hard nut to crack, ITTL they should me more likely to repell conquest attemps.