Well, the D5500 and D3300, built on the new monocoque body are only marginally more compact than the D5100 (which is my compact body, my big one is a D7200). However, since you have the D5100, I do know exactly which version of the 18-55 you have ... and that's where you can definitely save some weight and size substantially without a massive price penalty.
The two that come to mind are the 18-55 VR II and 55-200 VR II. They both use the same 52 mm thread and cap size (as does your existing 18-55 VR), so filters if you decide to use any are no problem, don't have super long zoom ranges and are sharp without any real optical flaws, and have collapsing lens barrels to keep things small and light. These two are designed to be used as a pair, giving you a normal zoom and a telephoto zoom lens. The best part, is that they're cheap, $130 refurbished direct from Nikon for the zooms (which is cheap enough that if it breaks you can just buy a new one). Links at the bottom, you can also sometimes find the refurbs even cheaper at major camera stores (the full price new is about $300 each).
I you want to go whole-hog, a D3300 kit includes both of the zoom lenses and gets you a second slightly smaller camera body for about $600 at most retailers, and it includes a Wi-Fi adapter to send to your phone.
If your budget is less forgiving, and you still want the telephoto reach, just pick up the 55-200 mm VR II, and you have a small, light lens that pairs really well with your 18-55, won't cost too much, is easy to carry and change over to when needed, and is very sharp. Just keep one on the camera and the other in your bag
http://www.nikonusa.com/en/Nikon-Products/Product/Refurbished-Camera-Lenses/AF-S-DX-NIKKOR-18-55mm-f%2F3.5-5.6G-VR-II-Refurbished.html
http://www.nikonusa.com/en/Nikon-Pr...R-55-200mm-f/4-5.6G-ED-VR-II-Refurbished.html
Edit: Also, if you want to shoot in low light or do macro, Nikon also makes three more lenses designed to work with that kit: one fast aperture (35 mm f/1.8 DX) and two macro (40 mm f/2.8 Micro and 85 mm f/3.5 VR Micro).
The two that come to mind are the 18-55 VR II and 55-200 VR II. They both use the same 52 mm thread and cap size (as does your existing 18-55 VR), so filters if you decide to use any are no problem, don't have super long zoom ranges and are sharp without any real optical flaws, and have collapsing lens barrels to keep things small and light. These two are designed to be used as a pair, giving you a normal zoom and a telephoto zoom lens. The best part, is that they're cheap, $130 refurbished direct from Nikon for the zooms (which is cheap enough that if it breaks you can just buy a new one). Links at the bottom, you can also sometimes find the refurbs even cheaper at major camera stores (the full price new is about $300 each).
I you want to go whole-hog, a D3300 kit includes both of the zoom lenses and gets you a second slightly smaller camera body for about $600 at most retailers, and it includes a Wi-Fi adapter to send to your phone.
If your budget is less forgiving, and you still want the telephoto reach, just pick up the 55-200 mm VR II, and you have a small, light lens that pairs really well with your 18-55, won't cost too much, is easy to carry and change over to when needed, and is very sharp. Just keep one on the camera and the other in your bag
http://www.nikonusa.com/en/Nikon-Products/Product/Refurbished-Camera-Lenses/AF-S-DX-NIKKOR-18-55mm-f%2F3.5-5.6G-VR-II-Refurbished.html
http://www.nikonusa.com/en/Nikon-Pr...R-55-200mm-f/4-5.6G-ED-VR-II-Refurbished.html
Edit: Also, if you want to shoot in low light or do macro, Nikon also makes three more lenses designed to work with that kit: one fast aperture (35 mm f/1.8 DX) and two macro (40 mm f/2.8 Micro and 85 mm f/3.5 VR Micro).