This paper presents a simple routing protocol based on topology control that improves the lifetime of a wireless sensor network in the usual convergecast pattern, by allowing the nodes to choose between two predefined power-levels to forward data towards the sink. The proposed protocol takes advantage of non-homogeneous topologies, where the nodes are grouped in clouds. Nodes will only use the highest power, to establish a link, when necessary, like for bridging the distance between two clouds. Within the clouds, only low-power links are used. The underlying distributed algorithm is shown to converge and finds, for each node of the network, an efficient path to the sink, provided the network is potentially connected at the highest of the two available transmission powers. We also propose a simple routing information refreshing technique that adds robustness to the proposed algorithm.