Ullmark is not going to get 8 million. Outside of very special cases, the ceiling for a goalie is about 6 million. 5.5 to 6.5 is the ballpark. There aren't many teams who can pay him that and also give up major assets to the Bruins.
Saros will get that because he is one of the few starters who has proven he can consistently handle a traditional starters workload (close to 70 games) and deliver elite numbers. This is in an era where true starters are becoming rarer and rarer, with most teams having tandems that more closely split games.
6M with term, signing bonuses, front loaded money, and a full NTC for at least part of the contract would already be legitimate top goalie money.
If there is a trade on the table and the Senators offer him something around 6M, 5 years, enough signing bonuses and front loaded money to make a buyout pointless, and a NMC for the first half of the contract - he has to strongly consider signing that because staying with the Bruins or getting traded somewhere to play out the year on a new system are both situations where he might see his market value lower after the season.
The odds of him getting much more than 6.5M next year aren't high, but the risk of injury or a drop in play will always be there. Especially after Swayman secured the net in the playoffs, or if he goes to a new system with worse defense.