The DIADEM project aims to develop assistive web-based technologies, in the form of an Expert System (ES), to improve online services access for older adults faced with cognitive decline. Both during the initial analysis and during system trials it is necessary to observe users browsing and interacting with ‘complex’ online forms. However, establishing what constitutes a ‘complex’ online form for this target user group, proved to be somewhat of a challenge. Consequently we have developed a set of Bespoke Online Form Selection (BOFS) metrics, which have been used to inform the online form selection and categorising process. BOFS has proved to be a valuable tool to identify complex online forms for use in DIADEM’s end-user trials. This paper presents the BOFS metrics, shows how these are aligned with the target user group, and demonstrates how BOFS has been of value within the context of the DIADEM project.