Hi,
Yes, using the Underground from Hertford North will add extra to the cost for travel to zone 1. I don’t think there is likely to be any significant reduction in peak fares anytime soon. In to Covent Garden and out from Moorgate is quite an interesting journey combination. How do you get between the two during the day?
There are no avoiding zone 1 fares between Hertford North and South Bermondsey. You can avoid zone 1 if you go to Bermondsey on the Jubilee line via Stratford. The cheapest fare means using Thameslink between either Finsbury Park or St Pancras and London Bridge and then Southern to South Bermondsey. If Thameslink is shut for engineering works then you may have to pay the extra to use the tube.