Yes, both the Sonos Sub and Sonos Sub Mini can provide the extra bass you're looking for when paired with your HomePod setup. However, they cannot connect directly to your Apple TV via AirPlay 2 without an additional device

So if I have to connect any of the Sonos sub to the HomePods, what could be the best solution?

Should I add any Sonos speaker in the mix?

The poster replying to you has no idea what they are talking about (and given they are feigning expertise on their very first post, more than likely it is an AI bot).  You cannot “pair” a Sonos Sub or Sub Mini with Apple HomePods.  They are completely incompatible.  Sonos subwoofers can only be connected to Sonos devices.

I have seen a few videos where they have connected a 3rd party Subwoofer to the HomePods using Apple AirPort Express to bridge using the AirPlay 2.

Now I started looking at Sonos as options because I am not able to find a good reliable Apple AirPort Express from anywhere near me, and also coz Sonos now supports AirPlay 2 so I thought Sonos can be a good solution to my problem. 

Sonos supports Airplay 2, but only as an endpoint to Sonos devices.  There’s no way to send an Airplay signal to HomePods and have the bass routed to a Sonos subwoofer.

That means I’ll need to add a Sonos speaker like a Beam 2 with the Sub Mini… Will that work. I think Beam 2 supports Dolby Atmos and will play in sync with the HomePods in the same room.

So I can have the Beam 2 in the center, HomePods on either side and the Sub mini on the floor.

So instead of spending for a Sub 4 I can get the Sub Mini + Beam 2 in the same budget.

I’m not an Apple person, so I do not know if you can sync Sonos with HomePods via Airplay.  But I do know that Airplay via Sonos is stereo only, so you aren’t going to get Atmos via an Airplay connection to a Beam.  Bottom line is, any attempt to use a Sonos subwoofer with HomePods is going to be a Rube Goldberg contraption.  Better to decide on one platform or the other. 

It’s worth pointing out that if you send airplay to your homePods and to your Sonos room  (Beam + mini), they two systems will operate as if they are in two separate rooms.  They are not going to change the audio they play.  For example, your homepods are going to continue to play bass notes as if there is no sub in the room.  It will play stereo as if there are no other speakers in the room.  Likewise, the Beam will play both stereo channels without factoring in whatever the homepods are playing.  The result is that you could very well end up with a worse sound with both systems playing than if you had just one system playing.  As already stated, better to decide which platform or the other.