There are a great many hotels within walking distance of the Informatics Forum. Edinburgh is generally a pleasant city to navigate on foot. The following are some suggestions, with approximate walking times according to Google Maps.

Hotel du Vin 4 min
Ten Hill Place 6 min
Residence Inn Edinburgh 6 min
Ibis Edinburgh Centre South Bridge 8 min
Edinburgh City Hotel 13 min
The Balmoral Hotel 16 min (Edinburgh's iconic hotel; expensive)
Best Western Plus Bruntsfield Hotel 20 min (pleasant walk across the Meadows)

Bed and Breakfast

There are also a huge number of bed and breakfast options near the Informatics Forum, particularly in the neighborhood of Newington to the southeast. Some representative options are listed below. We recommend using

Ellesmere House 16 min (pleasant walk across the Meadows)
Braveheart Guest House 17 min (walk along the side of the Meadows)
Auld Reekie Guest House 24 min
Barony House 24 min

Other options

There are university-run accommodation options, but they tend to be overpriced. Airbnb is a competitive option. Expect to pay £65-£85 per night (plus the usual Airbnb charges) for a full apartment within walking distance of the Forum.