The high concentration and rapid increase in lung diseases caused by COVID-19 has suddenly led medical staff to face a lack of ventilators in emergency situations. In this context, many enthusiasts and/or designers all over the world have started to think about low cost and open-source solutions for emergency ventilators, with the aim of providing concrete aid. In a small amount of time, many different solutions have been proposed, most of which are based on the automatic compression of the auxiliary manual breathing unit (AMBU) bag. In particular, many different designs have been conceived for the AMBU compression mechanism, which contains the most critical parts to be designed. Here arises the aim of this work, i.e., to propose a methodological approach to support the creativity of designers involved in inventing increasingly sustainable and reliable low-cost compression mechanisms for AMBU-based ventilators. Accordingly, a conceptual framework is proposed, capable of collecting existing ideas and organizing the underpinning concepts, to provide stimuli for new idea generation and to keep track of (and possibly to share) the explored design space. Illustrative examples are provided in order to show how the proposal can be used in practice. In particular, a set of currently available solutions is schematically shown through the proposed graphical tools, and the generation of new illustrative solutions is presented. Additionally, it is shown how to represent further ideas (e.g., those coming from other teams) in the framework.