2003 Honda Civic IMA P0134: Fixing O2 Sensor Circuit No Activity Detected - Bank 1 Sensor 1 Location & Cost Advice

I'm looking for help with a recurring P0134 fault on my 2003 Honda Civic IMA. The code 'O2 sensor circuit no activity detected' appears when the engine is cold, typically within the first kilometer of driving. If I reset the check engine light and drive the car while it's only warm (not fully warmed up), the warning light stays off. However, upon starting the vehicle in the morning with a cold engine, the code triggers shortly after startup. I initially tried disconnecting each oxygen sensor individually to identify which one was causing the issue, but this resulted in two different codes: P0135 and P0-141 — confirming that the problem may be related to multiple sensors or a wiring issue. I followed advice to clean my EGR valve, and surprisingly, after starting the engine, the P0134 code disappeared. I thought this would resolve it permanently, but the light returned the next morning. From research on this forum, I now understand that P0134 refers specifically to Bank 1 Sensor 1 — which is located in front of the catalytic converter (between the engine and the cat). My car has accumulated 185,000 miles, so I'm cautious about spending a lot. Honda dealerships have quoted extensive inspection fees, and OEM oxygen sensors cost around £200 each — making replacement expensive if I choose the wrong part. My main concern is whether this is simply a faulty sensor or something more complex. Given the mileage, I'd like to know if a simple sensor replacement could fix it without major repair costs. I appreciate any insights or troubleshooting tips from experienced users. Any advice would be greatly appreciated. Thanks, Steve