Buying a house, stuck in a tenancy!

We, myself (25F) and my partner (25M) are buying our first house in England, Hampshire. We have had our offer accepted at the start of January and are going through the motions with solicitors etc. As there is no chain on either side we are actually quite concerned that this is going to be a fairly straightforward and quick process (not normally what would concern buyers I'm sure!).

This is because we are locked into our 12 month tenancy with no break clause until the start of August, we have lived here for 3 years and stupidly didn't change to a monthly contract. We've asked twice now if the landlord would consider early release however on both occasions they have strongly rejected (and even cheekily offered for us to buy the flat we are renting from them...). We are hopeful that on the assurance of the estate agents and mortgage advisor it will take at least 4 months of conveyancing, which takes us to the start of May and then we can request to extend the completion date to somewhere between mid June-July, we can cover a month or two of overlapping rent and mortgage. The seller is abroad and the house is empty so we are assuming this wouldn't be a problem for them... (Hopefully).

However we are concerned that we might complete really soon, for example the end of February, making it really ridiculous to ask to complete in June and then we also risk the seller backing out to go back on the market.

Any advice on the tenancy or reassurances that conveyancing will take this long are appreciated! I think that's all the info but I can provide any more if there's questions :)