Half Fare card from hotel.

You can buy passes and tickets at the ticket office at Geneva Airport station. Not sure the extent of the half fare card offered by your b&b without knowing the details.

According to the leaflet I found here, the card entitles you to free transport (not half fare) in Interlaken and suburbs, but no further. This is common in Switzerland that if you stay in a town hotel it gives you free transport in that town or city.

I would recommend instead of a Swiss Travel pass, you buy a regional pass for the Berner Oberland (click here for details, CHF 240 for 4 days or CHF 300 for 6 days. This, unlike the Swiss Pass, covers the mountain railways.

You can buy all these passes when you get to Switzerland. Geneva airport (Genève-Aéroport) to Interlaken Ost costs CHF 73.

Thankyou so much for your help.... so the Regional pass is totally 'out of the Geneva airport area' hence I would still need to purchase transfers to and from the airport at additional costs?

Yes.
The fare from Genève-Aéroport (Geneva airport) to Interlaken Ost is 73 Franks and the trip takes about 3 hours. There are 2 trains per hour, changing at Bern.

The Berner Oberland Pass gives you full coverage on a different range of services than does the Swiss Travel Pass, but a 50% discount on the trains/lifts that are shown as dotted lines on their coverage map such as Muerren-Schilthorn and Kleine Scheidegg-Jungfraujoch.

By the look of things, it may actually be worth my while to invest in the 8 day Swiss Travel Pass then, (even tho I will be in Switzerland for only 6 days), - as my airport transfers will be covered in this cost, - and then I am not restricted to where I can travel to. Many thanks once again for all your helpful advice.