If you're only looking for which filter let's you blend in your clean bass, rather than filters which keep low end. There arnt too many!
In my experience most clean blends are done with band pass filters, as a low pass filter has plenty of bottom end.
Ones I've had/heard of with a clean blend
MXR BEF- Great sounding,bubbly,funky little filter. Is band pass,but great for finger funk tones. It isn't a hugely expensive pedal.
EBS Bass IQ- has an internal trimpot which allows you to dial in the clean high frequencies only, not a full range clean signal. Not too badly priced and has up/down sweep.
3 leaf Wonderlove/GR/GR2 - has clean blend and up/down and a lot of control. Currently very hard to find and expensive when you do.
EHX Qtron - big box/modern smaller version (not mini or micro)- very wet and lots of control, with up/downsweep. It has a "mix" mode which is 50/50 band pass and your clean bass signal. Fairly expensive if you can find one.
EHX Enigma Qballs- lots of control and a variable clean blend knob. In built distortion which isnt great. You can set the start/stop frequencies so you can get up/down sweep. A pig to dial in, but not mega money if you can find one used. There is also a Guitar tuned version called Riddle Qballs, which can be picked up fairly cheaply.
Source Audio Spectrum/C4 - loads and loads of filter models, sounds great. I can be set up via a PC or yiur mobile phone and has every parameter possible (incl clean blend) not mega money for what it gives you.
Subdecay Prometheus DLX- I've recently got this. All Analog and has up/down as well as dozens of step/pixelated/LFO And expression control (like a manual wah) it's synth heaven. It has low pass/band/high pass, however for bass players there is a,switch inside that adds clean blend to the band pass. Hard to get hold off and quite expensive.
Lovetone Meatball - good luck!!
Guyatone MR3- again good luck.
Exotic Robotalk 2- 2x band pass filters, each with a differnt tone. But both have a clean blend. Not too expensive.
Iron Ether - Xerograph deluxe- very synthy filter, has ton of control incl a clean blend. Fairly hard to get and expensive.
Seamoon Funk machine- a reverse sweep filter with a clean blend. Bit of a one trick pony, but very funky indeed. Quite expensive for what it does.
MXR Auto Q- more of an auto way than an envelope Filter,but has a clean blend and not expensive.
It all depends what you want a filter for. Low pass is all bottom end and great for adding to octave/fuzz to create synth sounds, however hard to dial in for finger funk. For the latter I prefer a band pass with a clean bass, sounds clean precise and funky,with no loss of bottom.
Another solution is to buy a boss LS2 and you can add a clean blend to any filter you like,as well as lots of very useful stuff 😁
IMO for what you're after the MXR is very hard to beat,Ive had 4, i keep selling them though, mustn't be enough and my C4 has a decent model of it.