Not sure if any of you are still thinking of possibilities, but here's one I've concocted for when I want to carry a filter on shorter trips, especially if with a group, and if I've decided to take my Platypus soft bottle with hose. This one is just a gravity filter; I haven't tried to use it in-line for sucking water through. It just happened to work with the resources I had readily available.
Take a look at the Platypus "Gravityworks" filter system.
It uses heavy Platy bags and it's expensive.
But, the filter itself is the same basic weight as all the others discussed here: mine weighs in at a bit under 2oz dry, a bit under 4oz wet. Good to .2 microns. Where I live in Canada, the MEC store has it for just over $40, which is about what we'd pay here to have one of the other slightly cheaper ones shipped, and have to wait forever for it to arrive in the mail. Perhaps one could use the platypus Cleanstream filter cartridge as well, if that's all that's available. Many of the others are not always readily available here.
I had an extra Platy tube + connectors laying around that I'd found at a discount store.
For the "dirty" bag, I substituted a large-size Ziploc, which weighs 13 grams and holds up to 4 liters. I snipped off a tiny piece of one of the lower corners.
I cut off the top of a water/soda bottle compatible with the Platypus screwcaps, put it into the bag, with the bottle neck gently pushed into the corner that was cut off, so that the open neck corresponds with the hole. (it should not go through the hole, however.)
I took my spare platy hose that screws onto a platy bottle, and cut the hose about 6 inches below the screw-on assemblage. This piece weighs about 11 grams.
I then screw on that bit of hose to the bottle neck, with the bag in the middle of them, held secure by them, if that makes sense. The water in the bag goes through the hole, down the hose. I can further secure the bottle-neck inside the bag by putting a rubber band or two around narrower parts of the neck where it will hold pretty well without cutting through the bag.
The Ziploc assemblage now functions as the "dirty" bag: You can (carefully) scoop up water with it and then close it, just like with the zip opening of the "dirty" bag. I can stop and start water flow with the little piece already used for that on my platypus that I'm already bringing.
I then stick the "dirty" end of the Gravityworks filter cartridge into the open end of the bit of tube, just as you'd stick it into the bit of tube coming out of the original "dirty" bag in the actual Gravityworks system.
Onto the "clean" end of the filter, I stick the end of my own platy hose with the mouthpiece temporarily removed. (Taking the mouthpiece/filter on and off is easy enough with my newer, "squishy" platy hose, but a bit more cumbersome with the older, firmer style.) The water would now go through the filter and into my platypus, or into the platypus or compatible water bottle of others in my group.
To get the "dirty" bag higher than the clean one for the gravity effect, gently wrap it in bandanna/clothing or something protective, and place it securely on a rock or soft log, etc. Or, bring a plastic grocery bag with a tiny hole in the bottom of it, and place the filled ziploc "dirty" bag in this bag with the hose sticking through the hole, then hang it with the grocery bag handles. You can multi-use the grocery bag(s) to store/organize something else in your pack if you want.
This system can work fine for a group, and filters much faster than those fancy pump filters my hiking buddies lug around.
If I'm already bringing my platypus and hose (or if someone else is), the rest of the assemblage weighs a bit over 3oz dry, and around 5oz when the filter is wet. If I'm hiking with someone whose a quick-disconnect style platypus, I may bring another snipped-off bit of hose with quick-disconnect end, weighing around .5oz, so they can filter directly to their platy without fussing with taking their mouthpiece off. And if sharing the weight of this filter system with one or two other people, you're each carrying only a couple ounces.
I specified "shorter trips" above, because obviously, the ziploc dirty bag setup is not as durable as the full-on Gravityworks system. You can tinker with ways to make it more durable. Sometimes I'm already carrying some food in another same-size Ziploc, and this would be my spare if the first one gets punctured. Or, I can just bring a spare Ziploc at a half-ounce penalty and use it to store clean water around camp. I bring some purification tabs as well, just in case.