Yes a full redemption in Avios is what you need to think about, so you may want to do the sums to see if buying some Avios is worth doing. Part payment isn't a good use of Avios, and buying Avios isn't usually a good idea either frankly, but if you have a hunch fares may get lower then it's useful to have a stack of Avios on call. That way you can get the assurance of a sealing your booking, and if fares come down you can strategically recover the Avios for another occasion, and benefit from the lower cash fares, for example in the next sale. Maybe something to bear in mind in the future. If you make a full redemption, choosing the minimum cash position (typically £1 or 50 pence on RFS fares) then all you lose is that small cash amount, all the Avios would come back to you - and normally it can all be done online too.

If waiting for a lower fare is proving stressful then buying at the current fares is an entirely logical thing to do since you're getting something for the money: reassurance of a confirmed booking.