Getting your source of good info and support in place before birth is invaluable.
If you can afford a lactation consultant that's probably the most efficient way. Go on the IBCLC website and use their search, then contact every one local to you and see which you get the best feeling from/find out their fee structure and waiting time if any. Hire one you feel comfortable with for a sort of "check up" home visit early on and/or get contact details so you can phone them up if you have any questions or problems.
If this is not affordable/as a supplement, look up whether you have a local branch of:
La Leche League
NCT
Association of Breastfeeding Mothers
Baby Café
And if you still have a Children's Centre see whether they have a breastfeeding support group/service.
Of course a lot of the in person groups will be closed at the moment, but you may still be able to access expert advice/support via these services on a one to one basis.
It should not be extremely painful - this was probably due to the tongue tie. It can be a bit painful to start but this should be for the first ten seconds of a feed, for the first ten days or so. You should be able to get past this by counting to ten. If it's painful throughout a feed, seek advice ASAP.
I'm a bit out of date on good BF books, but two I remember being good are The Food of Love, and The Womanly Art of Breastfeeding. Maybe there are better ones these days. Most likely your nearby specialists can advise :)
Getting shields no problem, but I wouldn't use them pre-emptively, as they can negatively affect feedback which is not great for supply. However if you're having pain and they help you to feed then that is an improvement.