Hi, I am an expert at this.
I do bank switching frequently, and moderate the UK Finance subreddit.
Join Chase, is my advice (there's also a £50 bonus for joining right now, so double bonus)...
Chase allow you to set up dummy accounts in an instant, then set up the account Direct Debits to Paypal, a spare ebay seller account (takes about 3-5 days), and/or Plum, which allows you to set up a £1 Direct Debit to your 'savings pot' there.
After you do this, it is a breeze, you can do bank switching from these accounts in an instant, without touching your 'main' bank account at all.
If you are not on Chase, use one of these codes when you sign up for the £50 bonus: TP9XPA, LK4685, WTQ5Y2, 69DHQU, VPDXZG.
Also for Plum use my referral if you like (but Plum isnt essential if you have a spare ebay, as usually you only need 2 DD) - https://friends.withplum.com/r/sVBYjT8XM0
Hope this helps. Let me know if you have any questions!