Wireless Body Area Network (WBAN) in recent years have received significant attention, due to their potential for increasing efficiency in healthcare monitoring. Typical sensors used for WBAN are low powered single transceiver devices utilizing a single channel for transmission at the Medium Access Control (MAC) layer. However, performance of these devices usually degrades when the density of sensors increases. One approach to counter this performance degradation is to exploit multiple channels at the MAC layer, where optimal usage of the channels is achieved through cooperation between the sensor nodes. In this paper we propose a cooperative WBAN environment that supports multi-hop transmission through cooperation involving both environmental sensors and WBAN nodes. Our solution extends the cooperation at the MAC layer to a cross-layered gradient based routing solution that allows interaction between WBAN and environmental sensors in order to ensure data delivery from WBANs to a distant gateway. Extensive simulations for healthcare scenarios have been performed to validate the cooperation at the MAC layer, as well as the cross-layered gradient based routing. Comparisons to other cooperative multi-channel MAC and routing solutions have shown the overall performance improvement of the proposed approach evaluated in terms of packet loss, power consumption and delay.