If you want a really good single conversion, check out the Berg. I've not used one but they are very good. What I like and I have one, is the FMA Diirect dual conversion receivers. They offer several that are .5oz. These are larger than the GWS but not by much. Try
www.fmadirect.com. They have an extremely small dual conversion 5 channel. I happen to have one of their 8 channel Quantums and it is also suitable for park flyers.