If by “threaded crank” you mean Hollowtech II, you have the following options:

- Put 24mm adapters in your BB30 bearings (I think Wheels mfg makes something like this). This is the least preferable but also the cheapest option. It lets you use your current bearings, probably.
- use a thread-together BB from Ceramicspeed, Token, Wheels mfg, Praxis etc. This is the most common option
- the best option, in my opinion, is to get a one piece aluminum bottom bracket from BBinfinite or Hambini. The bearings spin way better, last longer, and creak less. Hambini sells a BB for around $100, which is a lot, but it should last you a very long time and I think it’s a worthwhile upgrade.