Take a look at this article:

Best External Microphone for Sony Alpha Cameras – Camera Review

Sony Alpha cameras are industry leaders for video, but even a powerhouse like the A7 IV or A7S III falls short with inte…

www.cameraegg.org

Wind ruined my first vlog, so be careful. I would suggest:

• Rode VideoMic GO II Lightweight Shotgun Microphone Make sure to use the fluffy windscreen or youll regret it tbh.

^ This. Also, you should definitely check out the Sony ECM-G1 Vlogger Shotgun Microphone! It is fantastic for the a6400 because it uses the digital MI shoe. This means no messy cables or batteries since it draws power directly from your camera! It includes a fluffy windscreen which is amazing for that London wind. The shotgun design captures crystal clear audio from the front while blocking noise. Love it!

Look, if youre filming in London parks, wind is going to be your biggest hurdle. I've spent years testing different rigs and you really need something with a high signal-to-noise ratio so you arent fighting the a6400s weak internal preamps.

• Deity V-Mic D3 Pro Super-cardioid Shotgun Microphone: Best for your budget tbh. It has a step-less gain knob and long battery life. You can crank the mic gain and lower the camera volume in the settings to get rid of that scratchy hiss.
• <a href=" https://www.bhphotovideo.com/c/search?Ntt= Sennheiser+MKE+400+Compact+Shotgun+Microphone&BI=8941&KBID=10361&SID=12345&DFF=d50" target="_blank" rel="nofollow sponsored">Sennheiser MKE 400 Compact Shotgun Microphone: This one is solid because of the built-in shock mount and low-cut filter. When youre walking around, it filters out the low-end rumble from wind or distant city traffic. Whatever you pick, that fluffy thing is called a deadcat. Use it every time you go outside. If you see even a leaf moving on a tree, that wind muff needs to be on or your audio is basically toast. It just slides right over the mic.

Re: "Look, if youre filming in London parks, wind..."

• I have had nothing but issues with several setups that everyone swore were perfect for outdoor work. I spent a decent chunk of change on gear that was supposed to be professional grade, but unfortunately, the reliability was not as good as expected once I actually got out into the wind. It is incredibly frustrating when you think you have everything dialed in, only to get home and realize the audio is still unusable because the hardware couldnt handle the gusts. Before you spend your 150, are you planning on holding the camera at arms length the whole time, or will you be setting it up on a tripod further away? Also, is your main goal to just hear your voice clearly, or do you want to capture the background sounds of the park too? Your Sony Alpha a6400 can be picky with certain inputs, so knowing exactly how you move around will help avoid wasting money on gear that doesnt fit your style.

Works great for me