I think you should definitely try Seabourn. I spent a total of 50 days this year (2022) on the Odyssey and Sojourn. I've cruised on several HAL ships, but not since the pandemic. Seabourn is definitely a more luxurious experience. No crowds, excellent service, most everything included, no showing your key card, spacious suites, and more creative cooking. That said, my experience on the Odyssey was disappointing and I doubted I'd try Seabourn again. But when a friend told me she booked the Sojourn, I decided to give Seabourn a second chance. I'm glad I did, because that cruise was excellent. I would cruise Seabourn again.
As another poster mentioned, the dress code has just been relaxed. However, I would still guess that people would dress up more on Seabourn than on HAL. There will still be a formal night or two in the MDR, but there are more casual options as well. As far as accessibility goes, IME the majority of Seabourn passengers are 60+. And there were a number of wheelchairs, scooters, etc.
The lack of a real promenade deck is unfortunate, but there are numerous outdoor viewing areas as mentioned above. Deck 6 forward has a hot tub, loungers, and usually very few people. It was great for viewing the Panama Canal.
I think Alaska on Seabourn would be a very special experience. Good luck.
Bill