There is a significant overlap between people who are supported by income-related social welfare benefits, often in precarious situations, and those who experience greater digital exclusion. We report on a study of claimants using the UK's Universal Credit online welfare benefit system designed as, and still, "digital by default". Through data collection involving remote interviews (n=11) and online surveys (n=66), we expose claimants' own lived experiences interacting with this system. The claimants explain how digital channels can contribute to an imbalance of power and agency, at a time when their own circumstances mean they have reduced abilities, resources and capacities, and where design choices can adversely affect people's utility to leverage help from their own wider socio-technical ecosystems. We contribute eight recommendations from these accounts to inform the future design and development of digital welfare benefit systems for this population, to reduce digital barriers and harms.