As cited, The v800 is a good option, but some colleagues have had some trouble with the transmission of data. We continue to use the rs800cx, because we still think it is very reliable.
You can use the Firt Beat (https://www.firstbeat.com/en/) equipment, or eMotion sensor (http://www.megaemg.com/products/faros/). But I have had success using the RS800 or V800 from Polar. You can use Elite HRV app wtith cellphone or using the system from HRV4training (http://www.hrv4training.com/).
In case someone is still looking for a modern platform for HRV collection and analysis, then there is an Aidlab: https://www.aidlab.com/research (software+hardware)
Features: data exploration, analysis, data export, multiple biosignals collection, available on multiple platforms, also SDK is free to use for commercial projects.