How do I reduce deployment risk without slowing down releases?

Small and often; To reduce the risk of a deployment is to make each piece of work as small as possible. small change equals small risk. The same logic works for releases. This does mean you would have to increase the frequency of deployments and releases so that they are smaller and therefore lower risk.

In practice this means shipping single-feature or single-fix changesets — often behind a feature flag — rather than batching a week's work into one release: a change that touches one code path is much faster to review, test, and roll back if it turns out to be wrong.