General rule of thumb is that the weight of the lock is inversely proportional to the weight of the bike. Or more simply, lighter bike uses a heavier lock.

The lock I got for my Titanium bike is not light and you would probably not want it for that reason, but I bought a Bordo 6100. I wanted a combination lock and I did not want a big U lock, thus my choice for the Bordo. Comes in two lengths, I got the longer one. I think it is 1250 grams. It has about the same cabability as a U lock as far as size goes.
https://www.abus.com/eng/Mobile-Secu...RDO-Combo-6100

Most important thing is where you leave your bike. I live in Madison WI where there is a large university campus in the middle of town, plus there are some economically depressed high crime areas. In some of those areas you should not bring a nice bike. But other areas a bike can be left quite safe. Usually when I go to campus, I ride either my errand bike that I paid $5 for at a garage sale or another cheap bike. I do not ride my Titanium bike when I am going to campus.

And when you lock up your bike, if your front wheel is taken out of the fork and locked up with the frame, that would slow down most thieves, they want a fast getaway and reattaching a wheel would slow them down. That of course would scuff up your fork dropouts, but I have seen some cyclists do that where I used to work which was in a high theft area.

On some of my bikes I use a bolt on front skewer that uses a 5 mm allen wrench. I assume thieves are opportunists and do not carry around a 5 mm allen wrench with them. On bike tours with my Rohloff bike, I also use a bolt on skewer on the rear too. I keep a spare 5mm allen wrench with my spare tube in addition to my multitool, just in case I forgot the multitool at home the day I get a flat. I do not want to use something like a Pitlock, I am sure I would lose the key.