What pass fits best depends entirely on your travel plans. Use a planner, such as the DB planner or DB Navigator app to see how much time your journeys will take, so you have an idea of how much travel days you need. For domestic journeys in Sweden, it's best to use sj.se. Do not use the rail planner app (or the Interrail website) to plan, since they're not reliable enough for that purpose.

When are you planning the trip to Sweden? 

I suppose you need to take the train to Härnösand and then a bus from there to Skule. I don't have time to check the details right now as I am not at home. I'll give you more information in a few days.

The High Coast is a very nice area and I have been there many times.

Hi again!

To get to Skuleskogen you first need to take the train to Härnösand. From there you take the bus, which not is included in Interrail, to Skule. There are several bus stops where you can access Skuleskogen and there is also a special bus bringing hikers to different entry points of Skule. 

Here you can look for the bus between Härnösand and Skule (In Swedish)

https://www.dintur.se/navigation/sok-resa/

Here is information about the bus for hikers.

https://www.hogakusten.com/en/world-heritage-bus