Top-Up/Remortgage & Adding partner to mortgage

Looking for some advice on a mortgage top-up v remortgage. I bought a second hand property two years ago for €180,000.For this I recieved a mortgage of €100,000 and a loan from my parents of €80,000.
The house was in need of some repair so about €30,000 worth of upgrades were made to sort out the house.It was supposed to be an investment and be rented out. However circumstances changed between the partner and I(for the better) and we moved into the house.
Now we wish to carry out some more improvements ie build a garage and extend the drive.Also looking to pay my parents back a lump sum so overall looking for about 60,000-70,000.
Would it be more advisable to top-up with existing provider or look for a brand new mortgage? Since everything was in my name from day one if anything were to happen between my partner and I, she wouldnt have a leg to stand on. What is the procedure here? Would we have no choice but to remortgage to get her name specified on the house/mortgage?
Also how much would solictors cost for this procedure alone if we went down the Top-up route or would they be involved anyway .
Would this change in the mortgage affect the intrest relief. Would it be better to wait untill we get married ?
That wont be too far away as we are heading to Rome soon where I will ask her to marry me !!
I know before anyone says it...another good man gone !!
I know alot of questions but any advice appreciated as I would like some ammuntion if/when I go to BOI(my current provider)with any proposals...
Thanks

Can't answer everything here, but a few points:

A top -up generally does not involve a solicitor, an additional mortgage will. If you want to add your partner to the title and mortgage, you will need a solicitor, you will also need a new mortgage whether that be from your existing lender or not.

If you do add your partner to the title, you should safeguard the amount due ( or balance of same if you now repay part to them) to your parents in some way- perhaps by putting a second charge on the property in their favour.

Since everything was in my name from day one if anything were to happen between my partner and I, she wouldnt have a leg to stand on.

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I assume you mean if you continue as you presently are, with the property in your sole name. It would indeed be hard for her to establish a claim while you are unmarried, but once you marry it becomes your family home and therefore she may be entitled to an interest in it, depending on the circumstances when or if you split up.

Firstly thanks for the reply Vanilla
Looks like it will be a new mortgage so. Time to start looking around and getting together details of mortgage providers...again..
Was defo going to do something about the balance due to the parents all right. Forgive my ignorance but what do you mean by

Vanilla said:

perhaps by putting a second charge on the property in their favour.

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The solicitor we would be dealing with has been dealing with the family for years as my father is a local business man, so the solictor would hopefully do some kinda deal for us..again
What we were thinking in this regard is put somewhere on the contract that the parents would be owed €XXX if/when we move or split up. that might be what you meant Vanilla, Apologies if it is.

It would be a little like putting a mortgage on your title- except your parents charge would rank second to the mortgage ( otherwise the bank would not give you a mortgage as they must always rank first).

You could do a side agreement, many solicitors ( myself included) can be a little wary of their enforceability vis a vis family law rights. I'm sure your solicitor will give you all the advice necessary in any case.

Ok I think I get it now.Thanks vanilla. now comes the fun part !!
If we were to get the full remortgage how would that affect the the interest relief that I am currently recieving. I am thinking that I would lose some of as the mortgage would not now be classifed as a First Time buyer but I hope Im wrong on this